xxx

.github/workflows/build.yml

@@ -7,6 +7,7 @@ permissions:
   contents: read
 jobs:
   build:
+    if: github.repository == 'PicnicSupermarket/error-prone-support'
     strategy:
       matrix:
         os: [ ubuntu-22.04 ]

.github/workflows/codeql.yml

@@ -13,6 +13,7 @@ permissions:
   contents: read
 jobs:
   analyze:
+    if: github.repository == 'PicnicSupermarket/error-prone-support'
     strategy:
       matrix:
         language: [ java, ruby ]

.github/workflows/deploy-website.yml

@@ -9,6 +9,7 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
 jobs:
   build:
+    if: github.repository == 'PicnicSupermarket/error-prone-support'
     runs-on: ubuntu-22.04
     steps:
       - name: Install Harden-Runner

.github/workflows/openssf-scorecard.yml

@@ -14,6 +14,7 @@ permissions:
   contents: read
 jobs:
   analyze:
+    if: github.repository == 'PicnicSupermarket/error-prone-support'
     permissions:
       contents: read
       security-events: write

.github/workflows/pitest-analyze-pr.yml

@@ -9,6 +9,7 @@ permissions:
   contents: read
 jobs:
   analyze-pr:
+    if: github.repository == 'PicnicSupermarket/error-prone-support'
     runs-on: ubuntu-22.04
     steps:
       - name: Install Harden-Runner

.github/workflows/pitest-update-pr.yml

@@ -11,7 +11,7 @@ permissions:
   actions: read
 jobs:
   update-pr:
-    if: ${{ github.event.workflow_run.conclusion == 'success' }}
+    if: ${{ github.event.workflow_run.conclusion == 'success' && github.repository == 'PicnicSupermarket/error-prone-support' }}
     permissions:
       actions: read
       checks: write

.github/workflows/run-integration-tests.yml

@@ -9,13 +9,13 @@ name: "Integration tests"
 on:
   issue_comment:
     types: [ created ]
+  pull_request:
+  push:
 permissions:
   contents: read
 jobs:
   run-integration-tests:
     name: On-demand integration test
-    if: |
-      github.event.issue.pull_request && contains(github.event.comment.body, '/integration-test')
     runs-on: ubuntu-22.04
     steps:
       - name: Install Harden-Runner

integration-tests/checkstyle.sh

@@ -66,21 +66,23 @@ error_prone_patch_flags="${error_prone_shared_flags} -XepPatchLocation:IN_PLACE
      -path "*/META-INF/services/com.google.errorprone.bugpatterns.BugChecker" \
      -not -path "*/error-prone-experimental/*" \
      -not -path "*/error-prone-guidelines/*" \
+     -not -path "*/error-prone-contrib/*" \
      -print0 \
     | xargs -0 "${grep_command}" -hoP '[^.]+$' \
     | paste -s -d ',' -
-)"
+) -XepOpt:Refaster:NamePattern=.*Workshop.*"
 
 error_prone_validation_flags="${error_prone_shared_flags} -XepDisableAllChecks $(
   find "${error_prone_support_root}" \
      -path "*/META-INF/services/com.google.errorprone.bugpatterns.BugChecker" \
      -not -path "*/error-prone-experimental/*" \
      -not -path "*/error-prone-guidelines/*" \
+     -not -path "*/error-prone-contrib/*" \
      -print0 \
-    | xargs -0 "${grep_command}" -hoP '[^.]+$' \
+    | xargs -0 "${grep_command}" -hoP "[^.]+$' \
     | "${sed_command}" -r 's,(.*),-Xep:\1:WARN,' \
     | paste -s -d ' ' -
-)"
+) -XepOpt:Refaster:NamePattern=.*Workshop.*"
 
 echo "Shared build flags: ${shared_build_flags}"
 echo "Error Prone patch flags: ${error_prone_patch_flags}"
@@ -168,6 +170,7 @@ mvn ${shared_build_flags} \
       -Dtest='
         !MetadataGeneratorUtilTest#metadataFilesGenerationAllFiles,
         !XdocsJavaDocsTest#allCheckSectionJavaDocs' \
+      -Dstyle.color=always \
     | tee "${validation_build_log}" \
   || failure=1
 
@@ -191,12 +194,15 @@ else
   # XXX: This "diff of diffs" also contains vacuous sections, introduced due to
   # line offset differences. Try to omit those from the final output.
   if ! diff -u "${expected_changes}" "${actual_changes}"; then
-    echo 'There are unexpected changes. Inspect the preceding output for details.'
+    echo 'There are unexpected changes.'
+    echo "Inspect the changes here: ${report_directory}/${test_name}-diff-of-diffs-changes.patch"
+    diff -u "${expected_changes}" "${actual_changes}" > "${report_directory}/${test_name}-diff-of-diffs-changes.patch"
     failure=1
   fi
   echo 'Inspecting emitted warnings...'
   if ! diff -u "${expected_warnings}" "${actual_warnings}"; then
-    echo 'Diagnostics output changed. Inspect the preceding output for details.'
+    echo 'Diagnostics output changed.'
+    diff -u "${expected_warnings}" "${actual_warnings}" > "${report_directory}/${test_name}-diff-of-diffs-warnings.patch"
     failure=1
   fi
 fi

pom.xml

@@ -48,6 +48,7 @@
         <module>refaster-runner</module>
         <module>refaster-support</module>
         <module>refaster-test-support</module>
+        <module>workshop</module>
     </modules>
 
     <scm child.scm.developerConnection.inherit.append.path="false" child.scm.url.inherit.append.path="false">
@@ -409,14 +410,6 @@
                 <artifactId>byte-buddy</artifactId>
                 <version>1.14.13</version>
             </dependency>
-            <!-- Specified so that Renovate will file Maven upgrade PRs, which
-            subsequently will cause `maven-enforcer-plugin` to require that
-            developers build the project using the latest Maven release. -->
-            <dependency>
-                <groupId>org.apache.maven</groupId>
-                <artifactId>maven-plugin-api</artifactId>
-                <version>${version.maven}</version>
-            </dependency>
             <dependency>
                 <groupId>org.aspectj</groupId>
                 <artifactId>aspectjweaver</artifactId>
@@ -1041,9 +1034,6 @@
                             <requireJavaVersion>
                                 <version>${version.jdk}</version>
                             </requireJavaVersion>
-                            <requireMavenVersion>
-                                <version>${version.maven}</version>
-                            </requireMavenVersion>
                             <requireNoRepositories />
                             <requirePluginVersions />
                             <requireUpperBoundDeps />

workshop/README.md

@@ -0,0 +1,108 @@
+# Error Prone Workshop
+
+XXX: @Rick update the slides.
+
+## Initial setup of the workshop
+
+1. Start by cloning this repository locally from GitHub.
+2. Checkout the `workshop` branch.
+3. Make sure to run `mvn clean install` in the root of this repository.
+4. Open your code editor and familiarize yourself with the project structure.
+
+In IntelliJ IDEA (or your preferred editor), try to run the
+`WorkshopRefasterRulesTest` test. You might see the following error:
+
+```
+java: exporting a package from system module jdk.compiler is not allowed with --release
+```
+
+If this happens, go to _Settings -> Build, Execution, Deployment -> Compiler ->
+Java Compiler_ and deselect the option _Use '--release' option for
+cross-compilation (Java 9 and later)_.
+
+Now the project is ready for the workshop.
+
+## Part 1: Writing Refaster rules
+
+During this part of the workshop we will implement multiple Refaster rules.
+
+Go to the `workshop` module and open the
+`tech.picnic.errorprone.workshop.refasterrules` package. There you can find one
+example and 5 different exercises to do. Make sure to check out the
+`WorkshopRefasterRulesTest.java` class where you can enable tests. Per
+assignment there is a test in this class that one can enable (by dropping the
+`@Disabled` annotation) to validate your changes. The goal is to implement or
+improve the Refaster rules such that the enabled tests pass.
+
+Tips:
+
+* Go through the exercises in the proposed order.
+* The `XXX:` comments explains what needs to happen.
+* See the test cases for each Refaster rule by looking for the name of the
+  Refaster rule prefixed with `test`. For example, the
+  `WorkshopAssignment0Rules.java` rule collection has a Refaster rule named
+  `ExampleStringIsEmpty`. In the `WorkshopAssignment0RulesTestInput.java` and
+  `WorkshopAssignment0RulesTestOutput.java` files there is a
+  `testExampleStringIsEmpty` method that shows the input and output to test the
+  Refaster rule.
+
+## Part 2: Writing Error Prone checks
+
+During this part of the workshop we will implement parts of multiple Error
+Prone `BugChecker`s. Each of these classes contain `XXX` comments explaining
+what needs to be implemented. However, before diving in, make sure to first
+navigate to a check's associated test class to drop the class-level `@Disabled`
+annotation. Upon initial execution the tests will fail; the goal is to get then
+to pass.
+
+Some utility classes that you can use:
+
+* `com.google.errorprone.util.ASTHelpers`: contains many common operations on
+  the Abstract Syntax Tree.
+* `com.google.errorprone.fixes.SuggestedFixes`: contains helper methods for
+  creating `Fix`es.
+
+To see the impact of the newly introduced Error Prone checks [re-trigger the
+integration test framework](#validating-changes-with-the-integration-tests).
+
+## Part 3 (optional): Validating changes with the integration tests
+
+We created an integration testing framework that allows us to see the impact of
+the rules that are created. This testing framework can be executed locally and
+via GitHub Actions.
+
+If you still have more than 10-15 minutes left, and you want to test this
+locally, run the following commands:
+
+```sh
+mvn clean install -DskipTests -Dverification.skip
+./integration-tests/checkstyle-10.12.4.sh
+```
+
+Once the process is complete, and changes are introduced, the following output
+will be printed:
+
+```
+There are unexpected changes.
+Inspect the changes here: /tmp/tmp.Cmr423L1pA/checkstyle-10.12.4-diff-of-diffs-changes.patch
+```
+
+This file is be provided for your review using your preferred text editor.
+Alternatively, you can also navigate to the repository by going to the
+`./integration-tests/.repos/checkstyle` directory and executing `git log -p` to
+view the commit history and associated changes.
+
+This shows the impact of the rules that you wrote when they are applied to
+Checkstyle!
+
+The other option is to execute the integration test via GitHub Actions. You
+only need to commit and push to the branch. This will trigger execution of the
+integration tests, which will run for about 10 minutes. When the build is
+finished, go to the _Actions_ tab in your fork and navigate to your most recent
+commit and click on it. Then click on _Summary_ and download the artifact
+`integration-test-checkstyle-10.12.4` at the bottom. Once done, unzip the
+artifact and inspect the `checkstyle-10.12.4-diff-of-diffs-changes.patch` file
+to see the changes.
+
+[eps-github]: https://github.com/PicnicSupermarket/error-prone-support
+[eps-workshop-jfall]: https://drive.google.com/file/d/1Es1OuSUmPHSt3BjeCWfrXfoF-cJkkA1A/view

workshop/pom.xml

@@ -0,0 +1,150 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>tech.picnic.error-prone-support</groupId>
+        <artifactId>error-prone-support</artifactId>
+        <version>0.16.2-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>workshop</artifactId>
+
+    <name>Picnic :: Error Prone Support :: Workshop</name>
+    <description>Project for the Error Prone Workshop.</description>
+    <url>https://error-prone.picnic.tech</url>
+
+    <dependencies>
+        <dependency>
+            <groupId>${groupId.error-prone}</groupId>
+            <artifactId>error_prone_annotation</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>${groupId.error-prone}</groupId>
+            <artifactId>error_prone_annotations</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>${groupId.error-prone}</groupId>
+            <artifactId>error_prone_check_api</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>${groupId.error-prone}</groupId>
+            <artifactId>error_prone_core</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>${groupId.error-prone}</groupId>
+            <artifactId>error_prone_test_helpers</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>${project.groupId}</groupId>
+            <artifactId>error-prone-utils</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>${project.groupId}</groupId>
+            <artifactId>refaster-compiler</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>${project.groupId}</groupId>
+            <artifactId>refaster-support</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>${project.groupId}</groupId>
+            <artifactId>refaster-test-support</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.google.auto.service</groupId>
+            <artifactId>auto-service-annotations</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.aspectj</groupId>
+            <artifactId>aspectjweaver</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-params</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.openrewrite</groupId>
+            <artifactId>rewrite-core</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.openrewrite</groupId>
+            <artifactId>rewrite-java</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.openrewrite</groupId>
+            <artifactId>rewrite-java-11</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.openrewrite</groupId>
+            <artifactId>rewrite-templating</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-context</artifactId>
+            <scope>provided</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <pluginManagement>
+            <plugins>
+                <plugin>
+                    <groupId>org.apache.maven.plugins</groupId>
+                    <artifactId>maven-compiler-plugin</artifactId>
+                    <configuration>
+                        <annotationProcessorPaths combine.children="append">
+                            <path>
+                                <groupId>${project.groupId}</groupId>
+                                <artifactId>refaster-compiler</artifactId>
+                                <version>${project.version}</version>
+                            </path>
+                            <path>
+                                <groupId>${project.groupId}</groupId>
+                                <artifactId>refaster-support</artifactId>
+                                <version>${project.version}</version>
+                            </path>
+                        </annotationProcessorPaths>
+                        <compilerArgs combine.children="append">
+                            <arg>-Xplugin:RefasterRuleCompiler</arg>
+                        </compilerArgs>
+                    </configuration>
+                </plugin>
+            </plugins>
+        </pluginManagement>
+    </build>
+</project>

workshop/src/main/java/tech/picnic/errorprone/workshop/bugpatterns/Assignment0DeleteEmptyMethod.java

@@ -0,0 +1,33 @@
+package tech.picnic.errorprone.workshop.bugpatterns;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+
+import com.google.auto.service.AutoService;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
+import com.google.errorprone.matchers.Description;
+import com.sun.source.tree.MethodTree;
+
+/** A {@link BugChecker} that flags empty methods that seemingly can simply be deleted. */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Empty method can likely be deleted",
+    severity = WARNING,
+    tags = SIMPLIFICATION)
+public final class Assignment0DeleteEmptyMethod extends BugChecker implements MethodTreeMatcher {
+  private static final long serialVersionUID = 1L;
+
+  /** Instantiates a new {@link Assignment0DeleteEmptyMethod} instance. */
+  public Assignment0DeleteEmptyMethod() {}
+
+  @Override
+  public Description matchMethod(MethodTree tree, VisitorState state) {
+    // XXX: Part 1: Ensure that we only delete methods that contain no statements.
+    // XXX: Part 2: Don't delete methods that are annotated with `@Override`.
+
+    return Description.NO_MATCH;
+  }
+}

workshop/src/main/java/tech/picnic/errorprone/workshop/bugpatterns/Assignment1AssertJIsNullMethod.java

@@ -0,0 +1,61 @@
+package tech.picnic.errorprone.workshop.bugpatterns;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static com.google.errorprone.matchers.Matchers.allOf;
+import static com.google.errorprone.matchers.Matchers.argument;
+import static com.google.errorprone.matchers.Matchers.argumentCount;
+import static com.google.errorprone.matchers.Matchers.instanceMethod;
+import static com.google.errorprone.matchers.Matchers.nullLiteral;
+
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.sun.source.tree.MethodInvocationTree;
+
+/**
+ * A {@link BugChecker} that flags AssertJ {@code isEqualTo(null)} checks for simplification.
+ *
+ * <p>This bug checker cannot be replaced with a simple Refaster rule, as the Refaster approach
+ * would require that all overloads of {@link org.assertj.core.api.Assert#isEqualTo(Object)} (such
+ * as {@link org.assertj.core.api.AbstractStringAssert#isEqualTo(String)}) are explicitly
+ * enumerated. This bug checker generically matches all such current and future overloads.
+ */
+@BugPattern(
+    summary = "Prefer `.isNull()` over `.isEqualTo(null)`",
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class Assignment1AssertJIsNullMethod extends BugChecker
+    implements MethodInvocationTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<MethodInvocationTree> ASSERT_IS_EQUAL_TO_NULL =
+      allOf(
+          instanceMethod().onDescendantOf("org.assertj.core.api.Assert").named("isEqualTo"),
+          argumentCount(1),
+          argument(0, nullLiteral()));
+
+  /** Instantiates a new {@link Assignment1AssertJIsNullMethod} instance. */
+  public Assignment1AssertJIsNullMethod() {}
+
+  @Override
+  public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    // This statement filters out `MethodInvocation`s that are *not* `assertThat().isEqualTo(null)`
+    // statements.
+    if (!ASSERT_IS_EQUAL_TO_NULL.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    SuggestedFix.Builder fix = SuggestedFix.builder();
+
+    // XXX: Using `fix.merge(<some code>);` make sure we rename the method invocation to `isNull`.
+    // See the `SuggestedFixes` class ;).
+
+    tree.getArguments().forEach(arg -> fix.merge(SuggestedFix.delete(arg)));
+
+    return describeMatch(tree, fix.build());
+  }
+}

workshop/src/main/java/tech/picnic/errorprone/workshop/bugpatterns/Assignment2DropMockitoEq.java

@@ -0,0 +1,56 @@
+package tech.picnic.errorprone.workshop.bugpatterns;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static com.google.errorprone.matchers.Matchers.staticMethod;
+
+import com.google.common.collect.Iterables;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MethodInvocationTree;
+import tech.picnic.errorprone.utils.SourceCode;
+
+/**
+ * A {@link BugChecker} that flags method invocations for which all arguments are wrapped using
+ * {@link org.mockito.Mockito#eq}; this is redundant.
+ */
+@BugPattern(
+    summary = "Don't unnecessarily use Mockito's `eq(...)`",
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class Assignment2DropMockitoEq extends BugChecker
+    implements MethodInvocationTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<ExpressionTree> MOCKITO_EQ_METHOD =
+      staticMethod().onClass("org.mockito.ArgumentMatchers").named("eq");
+
+  /** Instantiates a new {@link Assignment2DropMockitoEq} instance. */
+  public Assignment2DropMockitoEq() {}
+
+  @Override
+  public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    // XXX: Make sure to return `Description.NO_MATCH` if the `tree` doesn't have arguments, or if
+    // the `isEqInvocation` method below returns `false` for at least one of the arguments.
+
+    SuggestedFix.Builder suggestedFix = SuggestedFix.builder();
+    for (ExpressionTree arg : tree.getArguments()) {
+      suggestedFix.replace(
+          arg,
+          SourceCode.treeToString(
+              Iterables.getOnlyElement(((MethodInvocationTree) arg).getArguments()), state));
+    }
+
+    return describeMatch(tree, suggestedFix.build());
+  }
+
+  @SuppressWarnings("UnusedMethod" /* Recommended to use when implementing this assignment. */)
+  private static boolean isEqInvocation(ExpressionTree tree, VisitorState state) {
+    return tree instanceof MethodInvocationTree && MOCKITO_EQ_METHOD.matches(tree, state);
+  }
+}

workshop/src/main/java/tech/picnic/errorprone/workshop/bugpatterns/Assignment3DropAutowiredConstructorAnnotation.java

@@ -0,0 +1,54 @@
+package tech.picnic.errorprone.workshop.bugpatterns;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static com.google.errorprone.matchers.ChildMultiMatcher.MatchType.AT_LEAST_ONE;
+import static com.google.errorprone.matchers.Matchers.annotations;
+import static com.google.errorprone.matchers.Matchers.isType;
+
+import com.google.common.collect.Iterables;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.ClassTreeMatcher;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.MultiMatcher;
+import com.google.errorprone.matchers.MultiMatcher.MultiMatchResult;
+import com.sun.source.tree.AnnotationTree;
+import com.sun.source.tree.ClassTree;
+import com.sun.source.tree.MethodTree;
+import com.sun.source.tree.Tree;
+import java.util.ArrayList;
+import java.util.List;
+import tech.picnic.errorprone.utils.SourceCode;
+
+/** A {@link BugChecker} that flags redundant {@code @Autowired} constructor annotations. */
+@BugPattern(
+    summary = "Omit `@Autowired` on a class' sole constructor, as it is redundant",
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class Assignment3DropAutowiredConstructorAnnotation extends BugChecker
+    implements ClassTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final MultiMatcher<Tree, AnnotationTree> AUTOWIRED_ANNOTATION =
+      annotations(AT_LEAST_ONE, isType("org.springframework.beans.factory.annotation.Autowired"));
+
+  /** Instantiates a new {@link Assignment3DropAutowiredConstructorAnnotation} instance. */
+  public Assignment3DropAutowiredConstructorAnnotation() {}
+
+  @Override
+  public Description matchClass(ClassTree tree, VisitorState state) {
+    // XXX: Using the `ASTHelpers#getConstructors` method, return `Description.NO_MATCH` if we do
+    // not have exactly 1 constructor (start by dropping `new ArrayList<>()` on the next line).
+    List<MethodTree> constructors = new ArrayList<>();
+
+    MultiMatchResult<AnnotationTree> hasAutowiredAnnotation =
+        AUTOWIRED_ANNOTATION.multiMatchResult(Iterables.getOnlyElement(constructors), state);
+    if (!hasAutowiredAnnotation.matches()) {
+      return Description.NO_MATCH;
+    }
+
+    AnnotationTree annotation = hasAutowiredAnnotation.onlyMatchingNode();
+    return describeMatch(annotation, SourceCode.deleteWithTrailingWhitespace(annotation, state));
+  }
+}

workshop/src/main/java/tech/picnic/errorprone/workshop/bugpatterns/Assignment4JUnitTestMethodDeclaration.java

@@ -0,0 +1,61 @@
+package tech.picnic.errorprone.workshop.bugpatterns;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static com.google.errorprone.matchers.ChildMultiMatcher.MatchType.AT_LEAST_ONE;
+import static com.google.errorprone.matchers.Matchers.annotations;
+import static com.google.errorprone.matchers.Matchers.anyOf;
+import static com.google.errorprone.matchers.Matchers.isType;
+
+import com.google.auto.service.AutoService;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Sets;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.MultiMatcher;
+import com.sun.source.tree.AnnotationTree;
+import com.sun.source.tree.MethodTree;
+import javax.lang.model.element.Modifier;
+
+/** A {@link BugChecker} that flags non-canonical JUnit method declarations. */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "JUnit method declaration can likely be improved",
+    severity = WARNING,
+    tags = SIMPLIFICATION)
+@SuppressWarnings({
+  "UnusedMethod",
+  "UnusedVariable"
+} /* This check is yet to be implemented as part of the demo. */)
+public final class Assignment4JUnitTestMethodDeclaration extends BugChecker
+    implements MethodTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final ImmutableSet<Modifier> ILLEGAL_MODIFIERS =
+      Sets.immutableEnumSet(Modifier.PRIVATE, Modifier.PROTECTED, Modifier.PUBLIC);
+  private static final MultiMatcher<MethodTree, AnnotationTree> TEST_METHOD =
+      annotations(AT_LEAST_ONE, anyOf(isType("org.junit.jupiter.api.Test")));
+
+  /** Instantiates a new {@link Assignment4JUnitTestMethodDeclaration} instance. */
+  public Assignment4JUnitTestMethodDeclaration() {}
+
+  @Override
+  public Description matchMethod(MethodTree tree, VisitorState state) {
+    // XXX: Part 1: Return `Description.NO_MATCH` if the method is not a `TEST_METHOD`.
+
+    SuggestedFix.Builder fixBuilder = SuggestedFix.builder();
+
+    // XXX: Part 2: Make sure that JUnit test methods don't use any of the modifiers from the
+    // `ILLEGAL_MODIFIERS` field, by using `SuggestedFixes#removeModifiers` and
+    // `SuggestedFix.Builder#merge`.
+
+    if (fixBuilder.isEmpty()) {
+      return Description.NO_MATCH;
+    }
+
+    return describeMatch(tree, fixBuilder.build());
+  }
+}

workshop/src/main/java/tech/picnic/errorprone/workshop/bugpatterns/Assignment5DeleteIdentityConversion.java

@@ -0,0 +1,108 @@
+package tech.picnic.errorprone.workshop.bugpatterns;
+
+import static com.google.common.collect.ImmutableSet.toImmutableSet;
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static com.google.errorprone.matchers.Matchers.anyOf;
+import static com.google.errorprone.matchers.Matchers.staticMethod;
+import static com.google.errorprone.suppliers.Suppliers.OBJECT_TYPE;
+
+import com.google.common.primitives.Primitives;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.bugpatterns.TypesWithUndefinedEquality;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.google.errorprone.util.ASTHelpers.TargetType;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MemberSelectTree;
+import com.sun.source.tree.MethodInvocationTree;
+import com.sun.tools.javac.code.Type;
+import com.sun.tools.javac.code.Types;
+import java.util.Arrays;
+import java.util.List;
+
+/** A {@link BugChecker} that flags redundant identity conversions. */
+@BugPattern(
+    summary = "Avoid or clarify identity conversions",
+    severity = WARNING,
+    tags = SIMPLIFICATION)
+public final class Assignment5DeleteIdentityConversion extends BugChecker
+    implements MethodInvocationTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<ExpressionTree> IS_CONVERSION_METHOD =
+      anyOf(
+          staticMethod()
+              .onClassAny(
+                  Primitives.allWrapperTypes().stream()
+                      .map(Class::getName)
+                      .collect(toImmutableSet()))
+              .named("valueOf"),
+          staticMethod().onClass(String.class.getName()).named("valueOf"),
+          staticMethod()
+              .onClassAny(
+                  "com.google.common.collect.ImmutableBiMap",
+                  "com.google.common.collect.ImmutableList",
+                  "com.google.common.collect.ImmutableListMultimap",
+                  "com.google.common.collect.ImmutableMap",
+                  "com.google.common.collect.ImmutableMultimap",
+                  "com.google.common.collect.ImmutableMultiset",
+                  "com.google.common.collect.ImmutableRangeMap",
+                  "com.google.common.collect.ImmutableRangeSet",
+                  "com.google.common.collect.ImmutableSet",
+                  "com.google.common.collect.ImmutableSetMultimap",
+                  "com.google.common.collect.ImmutableTable")
+              .named("copyOf"),
+          staticMethod()
+              .onClass("com.google.errorprone.matchers.Matchers")
+              .namedAnyOf("allOf", "anyOf"));
+
+  /** Instantiates a new {@link Assignment5DeleteIdentityConversion} instance. */
+  public Assignment5DeleteIdentityConversion() {}
+
+  @Override
+  public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    List<? extends ExpressionTree> arguments = tree.getArguments();
+    // XXX: Make sure we skip invocations that do not pass exactly one argument, by using the
+    // `tree`.
+    if (!IS_CONVERSION_METHOD.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    ExpressionTree sourceTree = arguments.get(0);
+    Type sourceType = ASTHelpers.getType(sourceTree);
+    Type resultType = ASTHelpers.getType(tree);
+    TargetType targetType = ASTHelpers.targetType(state);
+    if (sourceType == null || resultType == null || targetType == null) {
+      return Description.NO_MATCH;
+    }
+
+    if (!state.getTypes().isSameType(sourceType, resultType)
+        && !isConvertibleWithWellDefinedEquality(sourceType, targetType.type(), state)) {
+      return Description.NO_MATCH;
+    }
+
+    if (sourceType.isPrimitive()
+        && state.getPath().getParentPath().getLeaf() instanceof MemberSelectTree) {
+      return Description.NO_MATCH;
+    }
+
+    return buildDescription(tree)
+        // XXX: Use the `.addFix()` to suggest replacing the original `tree` with the `sourceTree`.
+        // Tip: You can get the actual String representation of a Tree by using the
+        // `SourceCode#treeToString`.
+        .build();
+  }
+
+  private static boolean isConvertibleWithWellDefinedEquality(
+      Type sourceType, Type targetType, VisitorState state) {
+    Types types = state.getTypes();
+    return !types.isSameType(targetType, OBJECT_TYPE.get(state))
+        && types.isConvertible(sourceType, targetType)
+        && Arrays.stream(TypesWithUndefinedEquality.values())
+            .noneMatch(b -> b.matchesType(sourceType, state) || b.matchesType(targetType, state));
+  }
+}

workshop/src/main/java/tech/picnic/errorprone/workshop/refasterrules/WorkshopAssignment0Rules.java

@@ -0,0 +1,22 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+
+/** Refaster rule used as example for the assignments of the workshop. */
+final class WorkshopAssignment0Rules {
+  private WorkshopAssignment0Rules() {}
+
+  /** Prefer {@link String#isEmpty()} over alternatives that consult the string's length. */
+  static final class ExampleStringIsEmpty {
+    @BeforeTemplate
+    static boolean before(String string) {
+      return string.length() == 0;
+    }
+
+    @AfterTemplate
+    static boolean after(String string) {
+      return string.isEmpty();
+    }
+  }
+}

workshop/src/main/java/tech/picnic/errorprone/workshop/refasterrules/WorkshopAssignment1Rules.java

@@ -0,0 +1,11 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+/** Refaster rules for the first assignment of the workshop. */
+final class WorkshopAssignment1Rules {
+  private WorkshopAssignment1Rules() {}
+
+  /** Prefer {@link String#String(char[])} over {@link String#copyValueOf(char[])}. */
+  static final class NewStringCharArray {
+    // XXX: Implement this Refaster rule.
+  }
+}

workshop/src/main/java/tech/picnic/errorprone/workshop/refasterrules/WorkshopAssignment2Rules.java

@@ -0,0 +1,34 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+import com.google.common.collect.ImmutableList;
+import com.google.errorprone.refaster.Refaster;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+
+import java.util.Collections;
+import java.util.List;
+
+/** Refaster rules for the second assignment of the workshop. */
+final class WorkshopAssignment2Rules {
+  private WorkshopAssignment2Rules() {}
+
+  /**
+   * Prefer {@link ImmutableList#of(Object)} over alternatives that don't communicate the
+   * immutability of the resulting list at the type level.
+   */
+  static final class ImmutableListOfOne<T> {
+    @BeforeTemplate
+    static <T> List<T> before(T t) {
+      return ImmutableList.copyOf(
+          Refaster.anyOf(
+              Collections.singletonList(t),
+              List.of(t))
+      );
+    }
+
+    @AfterTemplate
+    static <T> List<T> after(T t) {
+      return ImmutableList.of(t);
+    }
+  }
+}

workshop/src/main/java/tech/picnic/errorprone/workshop/refasterrules/WorkshopAssignment3Rules.java

@@ -0,0 +1,21 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+import com.google.common.base.Preconditions;
+
+/** Refaster rules for the third assignment of the workshop. */
+@SuppressWarnings("UnusedTypeParameter" /* Ignore this for demo purposes. */)
+final class WorkshopAssignment3Rules {
+  private WorkshopAssignment3Rules() {}
+
+  // XXX: Tip: check the input and output files to see the *expected* refactoring.
+
+  /** Prefer {@link Preconditions#checkArgument(boolean)} over if statements. */
+  static final class CheckArgumentWithoutMessage {
+    // XXX: Implement the Refaster rule to get the test green.
+  }
+
+  /** Prefer {@link Preconditions#checkArgument(boolean, Object)} over if statements. */
+  static final class CheckArgumentWithMessage {
+    // XXX: Implement the Refaster rule to get the test green.
+  }
+}

workshop/src/main/java/tech/picnic/errorprone/workshop/refasterrules/WorkshopAssignment4Rules.java

@@ -0,0 +1,25 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+/** Refaster rules for the fourth assignment of the workshop. */
+@SuppressWarnings("java:S1698" /* Reference comparison is valid for enums. */)
+final class WorkshopAssignment4Rules {
+  private WorkshopAssignment4Rules() {}
+
+  // The test fails because non Enum comparisons are also rewritten.
+  // Fix the test by tweaking the type parameters.
+
+  // XXX: Get the test to pass by improving the Refaster rule (uncommented it first).
+
+  //  static final class PrimitiveOrReferenceEqualityEnum<T> {
+  //    @BeforeTemplate
+  //    boolean before(T a, T b) {
+  //      return Refaster.anyOf(a.equals(b), Objects.equals(a, b));
+  //    }
+  //
+  //    @AfterTemplate
+  //    @AlsoNegation
+  //    boolean after(T a, T b) {
+  //      return a == b;
+  //    }
+  //  }
+}

workshop/src/main/java/tech/picnic/errorprone/workshop/refasterrules/WorkshopAssignment5Rules.java

@@ -0,0 +1,12 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+/** Refaster rules for the fifth assignment of the workshop. */
+@SuppressWarnings("UnusedTypeParameter" /* Ignore this for demo purposes. */)
+final class WorkshopAssignment5Rules {
+  private WorkshopAssignment5Rules() {}
+
+  abstract static class StreamDoAllMatch<T> {
+    // XXX: Implement the Refaster rule to get the test green.
+    // Tip: use the `@Placeholder` annotation.
+  }
+}

workshop/src/test/java/tech/picnic/errorprone/workshop/bugpatterns/Assignment0Assignment0DeleteEmptyMethodTest.java

@@ -0,0 +1,70 @@
+package tech.picnic.errorprone.workshop.bugpatterns;
+
+import com.google.errorprone.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+
+@Disabled("Enable this when implementing the BugChecker.")
+final class Assignment0Assignment0DeleteEmptyMethodTest {
+  @Test
+  void identification() {
+    CompilationTestHelper.newInstance(Assignment0DeleteEmptyMethod.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "class A {",
+            "  Object m1() {",
+            "    return null;",
+            "  }",
+            "",
+            "  void m2() {",
+            "    System.out.println(42);",
+            "  }",
+            "",
+            "  // BUG: Diagnostic contains:",
+            "  static void m3() {}",
+            "",
+            "  interface F {",
+            "    void fun();",
+            "  }",
+            "}")
+        .addSourceLines(
+            "B.java",
+            "final class B implements A.F {",
+            "  @Override",
+            "  public void fun() {}",
+            "",
+            "  /** Javadoc. */",
+            "  // BUG: Diagnostic contains:",
+            "  void m4() {}",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  void replacement() {
+    BugCheckerRefactoringTestHelper.newInstance(Assignment0DeleteEmptyMethod.class, getClass())
+        .addInputLines(
+            "A.java",
+            "final class A {",
+            "",
+            "  void instanceMethod() {}",
+            "",
+            "  static void staticMethod() {}",
+            "",
+            "  static void staticMethodWithComment() {",
+            "    System.out.println(42);",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "final class A {",
+            "",
+            "  static void staticMethodWithComment() {",
+            "    System.out.println(42);",
+            "  }",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+}

workshop/src/test/java/tech/picnic/errorprone/workshop/bugpatterns/Assignment1AssertJIsNullMethodTest.java

@@ -0,0 +1,60 @@
+package tech.picnic.errorprone.workshop.bugpatterns;
+
+import com.google.errorprone.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+
+@Disabled("Enable this when implementing the BugChecker.")
+final class Assignment1AssertJIsNullMethodTest {
+  @Test
+  void identification() {
+    CompilationTestHelper.newInstance(Assignment1AssertJIsNullMethod.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "import static org.assertj.core.api.Assertions.assertThat;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    assertThat(1).isEqualTo(1);",
+            "    // BUG: Diagnostic contains:",
+            "    assertThat(1).isEqualTo(null);",
+            "    // BUG: Diagnostic contains:",
+            "    assertThat(\"foo\").isEqualTo(null);",
+            "    isEqualTo(null);",
+            "  }",
+            "",
+            "  private boolean isEqualTo(Object value) {",
+            "    return value.equals(\"bar\");",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  void replacement() {
+    BugCheckerRefactoringTestHelper.newInstance(Assignment1AssertJIsNullMethod.class, getClass())
+        .addInputLines(
+            "A.java",
+            "import static org.assertj.core.api.Assertions.assertThat;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    assertThat(1).isEqualTo(null);",
+            "    assertThat(\"foo\").isEqualTo(null);",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "import static org.assertj.core.api.Assertions.assertThat;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    assertThat(1).isNull();",
+            "    assertThat(\"foo\").isNull();",
+            "  }",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+}

workshop/src/test/java/tech/picnic/errorprone/workshop/bugpatterns/Assignment2DropMockitoEqTest.java

@@ -0,0 +1,102 @@
+package tech.picnic.errorprone.workshop.bugpatterns;
+
+import com.google.errorprone.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+
+@Disabled("Enable this when implementing the BugChecker.")
+final class Assignment2DropMockitoEqTest {
+  @Test
+  void identification() {
+    CompilationTestHelper.newInstance(Assignment2DropMockitoEq.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "import static org.mockito.ArgumentMatchers.eq;",
+            "import static org.mockito.ArgumentMatchers.notNull;",
+            "import static org.mockito.Mockito.doAnswer;",
+            "import static org.mockito.Mockito.mock;",
+            "",
+            "import java.util.function.BiConsumer;",
+            "import java.util.function.Consumer;",
+            "import org.mockito.ArgumentMatchers;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Runnable runnable = mock(Runnable.class);",
+            "    doAnswer(inv -> null).when(runnable).run();",
+            "",
+            "    Consumer<String> consumer = mock(Consumer.class);",
+            "    doAnswer(inv -> null).when(consumer).accept(\"foo\");",
+            "    doAnswer(inv -> null).when(consumer).accept(notNull());",
+            "    // BUG: Diagnostic contains:",
+            "    doAnswer(inv -> null).when(consumer).accept(ArgumentMatchers.eq(\"foo\"));",
+            "    // BUG: Diagnostic contains:",
+            "    doAnswer(inv -> null).when(consumer).accept(eq(toString()));",
+            "",
+            "    BiConsumer<Integer, String> biConsumer = mock(BiConsumer.class);",
+            "    doAnswer(inv -> null).when(biConsumer).accept(0, \"foo\");",
+            "    doAnswer(inv -> null).when(biConsumer).accept(eq(0), notNull());",
+            "    doAnswer(inv -> null).when(biConsumer).accept(notNull(), eq(\"foo\"));",
+            "    doAnswer(inv -> null)",
+            "        .when(biConsumer)",
+            "        // BUG: Diagnostic contains:",
+            "        .accept(ArgumentMatchers.eq(0), ArgumentMatchers.eq(\"foo\"));",
+            "    // BUG: Diagnostic contains:",
+            "    doAnswer(inv -> null).when(biConsumer).accept(eq(hashCode()), eq(toString()));",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  void replacement() {
+    BugCheckerRefactoringTestHelper.newInstance(Assignment2DropMockitoEq.class, getClass())
+        .addInputLines(
+            "A.java",
+            "import static org.mockito.ArgumentMatchers.eq;",
+            "import static org.mockito.Mockito.doAnswer;",
+            "import static org.mockito.Mockito.mock;",
+            "",
+            "import java.util.function.BiConsumer;",
+            "import java.util.function.Consumer;",
+            "import org.mockito.ArgumentMatchers;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Consumer<String> consumer = mock(Consumer.class);",
+            "    doAnswer(inv -> null).when(consumer).accept(ArgumentMatchers.eq(\"foo\"));",
+            "    doAnswer(inv -> null).when(consumer).accept(eq(toString()));",
+            "",
+            "    BiConsumer<Integer, String> biConsumer = mock(BiConsumer.class);",
+            "    doAnswer(inv -> null)",
+            "        .when(biConsumer)",
+            "        .accept(ArgumentMatchers.eq(0), ArgumentMatchers.eq(\"foo\"));",
+            "    doAnswer(inv -> null).when(biConsumer).accept(eq(hashCode()), eq(toString()));",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "import static org.mockito.ArgumentMatchers.eq;",
+            "import static org.mockito.Mockito.doAnswer;",
+            "import static org.mockito.Mockito.mock;",
+            "",
+            "import java.util.function.BiConsumer;",
+            "import java.util.function.Consumer;",
+            "import org.mockito.ArgumentMatchers;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Consumer<String> consumer = mock(Consumer.class);",
+            "    doAnswer(inv -> null).when(consumer).accept(\"foo\");",
+            "    doAnswer(inv -> null).when(consumer).accept(toString());",
+            "",
+            "    BiConsumer<Integer, String> biConsumer = mock(BiConsumer.class);",
+            "    doAnswer(inv -> null).when(biConsumer).accept(0, \"foo\");",
+            "    doAnswer(inv -> null).when(biConsumer).accept(hashCode(), toString());",
+            "  }",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+}

workshop/src/test/java/tech/picnic/errorprone/workshop/bugpatterns/Assignment3DropAutowiredConstructorAnnotationTest.java

@@ -0,0 +1,106 @@
+package tech.picnic.errorprone.workshop.bugpatterns;
+
+import com.google.errorprone.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+
+@Disabled("Enable this when implementing the BugChecker.")
+final class Assignment3DropAutowiredConstructorAnnotationTest {
+  @Test
+  void identification() {
+    CompilationTestHelper.newInstance(
+            Assignment3DropAutowiredConstructorAnnotation.class, getClass())
+        .addSourceLines(
+            "Container.java",
+            "import com.google.errorprone.annotations.Immutable;",
+            "import java.util.List;",
+            "import org.springframework.beans.factory.annotation.Autowired;",
+            "",
+            "interface Container {",
+            "  @Immutable",
+            "  class A {",
+            "    A() {}",
+            "  }",
+            "",
+            "  class B {",
+            "    @Autowired",
+            "    void setProperty(Object o) {}",
+            "  }",
+            "",
+            "  class C {",
+            "    // BUG: Diagnostic contains:",
+            "    @Autowired",
+            "    C() {}",
+            "  }",
+            "",
+            "  class D {",
+            "    // BUG: Diagnostic contains:",
+            "    @Autowired",
+            "    D(String x) {}",
+            "  }",
+            "",
+            "  class E {",
+            "    @Autowired",
+            "    E() {}",
+            "",
+            "    E(String x) {}",
+            "  }",
+            "",
+            "  class F {",
+            "    F() {}",
+            "",
+            "    @Autowired",
+            "    F(String x) {}",
+            "  }",
+            "",
+            "  class G {",
+            "    @Autowired private Object o;",
+            "  }",
+            "",
+            "  class H {",
+            "    @SafeVarargs",
+            "    H(List<String>... lists) {}",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  void replacement() {
+    BugCheckerRefactoringTestHelper.newInstance(
+            Assignment3DropAutowiredConstructorAnnotation.class, getClass())
+        .addInputLines(
+            "Container.java",
+            "import org.springframework.beans.factory.annotation.Autowired;",
+            "",
+            "interface Container {",
+            "  class A {",
+            "    @Autowired",
+            "    @Deprecated",
+            "    A() {}",
+            "  }",
+            "",
+            "  class B {",
+            "    @Autowired",
+            "    B(String x) {}",
+            "  }",
+            "}")
+        .addOutputLines(
+            "Container.java",
+            "import org.springframework.beans.factory.annotation.Autowired;",
+            "",
+            "interface Container {",
+            "  class A {",
+            "    @Deprecated",
+            "    A() {}",
+            "  }",
+            "",
+            "  class B {",
+            "    B(String x) {}",
+            "  }",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+}

workshop/src/test/java/tech/picnic/errorprone/workshop/bugpatterns/Assignment4JUnitTestMethodDeclarationTest.java

@@ -0,0 +1,91 @@
+package tech.picnic.errorprone.workshop.bugpatterns;
+
+import com.google.errorprone.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+
+@Disabled("Enable this to validate part 1.")
+final class Assignment4JUnitTestMethodDeclarationTest {
+  @Test
+  void identificationIllegalModifiers() {
+    CompilationTestHelper.newInstance(Assignment4JUnitTestMethodDeclaration.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "import org.junit.jupiter.api.Test;",
+            "",
+            "class A {",
+            "  @Test",
+            "  void method1() {}",
+            "",
+            "  @Test",
+            "  // BUG: Diagnostic contains:",
+            "  public void method2() {}",
+            "",
+            "  @Test",
+            "  // BUG: Diagnostic contains:",
+            "  protected void method3() {}",
+            "",
+            "  @Test",
+            "  // BUG: Diagnostic contains:",
+            "  private void method4() {}",
+            "",
+            "  public void method5() {}",
+            "",
+            "  protected void method6() {}",
+            "",
+            "  private void method7() {}",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  void replacementIllegalModifiers() {
+    BugCheckerRefactoringTestHelper.newInstance(
+            Assignment4JUnitTestMethodDeclaration.class, getClass())
+        .addInputLines(
+            "A.java",
+            "import org.junit.jupiter.api.Test;",
+            "",
+            "class A {",
+            "  @Test",
+            "  void foo() {}",
+            "",
+            "  @Test",
+            "  public void bar() {}",
+            "",
+            "  @Test",
+            "  protected void baz() {}",
+            "",
+            "  @Test",
+            "  private void qux() {}",
+            "",
+            "  public void quux() {}",
+            "",
+            "  private void quuz() {}",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "import org.junit.jupiter.api.Test;",
+            "",
+            "class A {",
+            "  @Test",
+            "  void foo() {}",
+            "",
+            "  @Test",
+            "  void bar() {}",
+            "",
+            "  @Test",
+            "  void baz() {}",
+            "",
+            "  @Test",
+            "  void qux() {}",
+            "",
+            "  public void quux() {}",
+            "",
+            "  private void quuz() {}",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+}

workshop/src/test/java/tech/picnic/errorprone/workshop/bugpatterns/Assignment5DeleteIdentityConversionTest.java

@@ -0,0 +1,223 @@
+package tech.picnic.errorprone.workshop.bugpatterns;
+
+import com.google.errorprone.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+
+@Disabled("Enable this when implementing the BugChecker.")
+final class Assignment5DeleteIdentityConversionTest {
+  @Test
+  void identification() {
+    CompilationTestHelper.newInstance(Assignment5DeleteIdentityConversion.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "import static com.google.errorprone.matchers.Matchers.instanceMethod;",
+            "import static com.google.errorprone.matchers.Matchers.staticMethod;",
+            "",
+            "import com.google.common.collect.ImmutableBiMap;",
+            "import com.google.common.collect.ImmutableList;",
+            "import com.google.common.collect.ImmutableListMultimap;",
+            "import com.google.common.collect.ImmutableMap;",
+            "import com.google.common.collect.ImmutableMultimap;",
+            "import com.google.common.collect.ImmutableMultiset;",
+            "import com.google.common.collect.ImmutableRangeMap;",
+            "import com.google.common.collect.ImmutableRangeSet;",
+            "import com.google.common.collect.ImmutableSet;",
+            "import com.google.common.collect.ImmutableSetMultimap;",
+            "import com.google.common.collect.ImmutableTable;",
+            "import com.google.errorprone.matchers.Matcher;",
+            "import com.google.errorprone.matchers.Matchers;",
+            "",
+            "public final class A {",
+            "  public void m() {",
+            "    // BUG: Diagnostic contains:",
+            "    Matcher allOf1 = Matchers.allOf(instanceMethod());",
+            "    Matcher allOf2 = Matchers.allOf(instanceMethod(), staticMethod());",
+            "    // BUG: Diagnostic contains:",
+            "    Matcher anyOf1 = Matchers.anyOf(staticMethod());",
+            "    Matcher anyOf2 = Matchers.anyOf(instanceMethod(), staticMethod());",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Boolean b1 = Boolean.valueOf(Boolean.FALSE);",
+            "    // BUG: Diagnostic contains:",
+            "    Boolean b2 = Boolean.valueOf(false);",
+            "    // BUG: Diagnostic contains:",
+            "    boolean b3 = Boolean.valueOf(Boolean.FALSE);",
+            "    // BUG: Diagnostic contains:",
+            "    boolean b4 = Boolean.valueOf(false);",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Byte byte1 = Byte.valueOf((Byte) Byte.MIN_VALUE);",
+            "    // BUG: Diagnostic contains:",
+            "    Byte byte2 = Byte.valueOf(Byte.MIN_VALUE);",
+            "    // BUG: Diagnostic contains:",
+            "    byte byte3 = Byte.valueOf((Byte) Byte.MIN_VALUE);",
+            "    // BUG: Diagnostic contains:",
+            "    byte byte4 = Byte.valueOf(Byte.MIN_VALUE);",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Character c1 = Character.valueOf((Character) 'a');",
+            "    // BUG: Diagnostic contains:",
+            "    Character c2 = Character.valueOf('a');",
+            "    // BUG: Diagnostic contains:",
+            "    char c3 = Character.valueOf((Character) 'a');",
+            "    // BUG: Diagnostic contains:",
+            "    char c4 = Character.valueOf('a');",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Double d1 = Double.valueOf((Double) 0.0);",
+            "    // BUG: Diagnostic contains:",
+            "    Double d2 = Double.valueOf(0.0);",
+            "    // BUG: Diagnostic contains:",
+            "    double d3 = Double.valueOf((Double) 0.0);",
+            "    // BUG: Diagnostic contains:",
+            "    double d4 = Double.valueOf(0.0);",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Float f1 = Float.valueOf((Float) 0.0F);",
+            "    // BUG: Diagnostic contains:",
+            "    Float f2 = Float.valueOf(0.0F);",
+            "    // BUG: Diagnostic contains:",
+            "    float f3 = Float.valueOf((Float) 0.0F);",
+            "    // BUG: Diagnostic contains:",
+            "    float f4 = Float.valueOf(0.0F);",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Integer i1 = Integer.valueOf((Integer) 1);",
+            "    // BUG: Diagnostic contains:",
+            "    Integer i2 = Integer.valueOf(1);",
+            "    // BUG: Diagnostic contains:",
+            "    int i3 = Integer.valueOf((Integer) 1);",
+            "    // BUG: Diagnostic contains:",
+            "    int i4 = Integer.valueOf(1);",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Long l1 = Long.valueOf((Long) 1L);",
+            "    // BUG: Diagnostic contains:",
+            "    Long l2 = Long.valueOf(1L);",
+            "    // BUG: Diagnostic contains:",
+            "    long l3 = Long.valueOf((Long) 1L);",
+            "    // BUG: Diagnostic contains:",
+            "    long l4 = Long.valueOf(1L);",
+            "",
+            "    Long l5 = Long.valueOf((Integer) 1);",
+            "    Long l6 = Long.valueOf(1);",
+            "    // BUG: Diagnostic contains:",
+            "    long l7 = Long.valueOf((Integer) 1);",
+            "    // BUG: Diagnostic contains:",
+            "    long l8 = Long.valueOf(1);",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Short s1 = Short.valueOf((Short) Short.MIN_VALUE);",
+            "    // BUG: Diagnostic contains:",
+            "    Short s2 = Short.valueOf(Short.MIN_VALUE);",
+            "    // BUG: Diagnostic contains:",
+            "    short s3 = Short.valueOf((Short) Short.MIN_VALUE);",
+            "    // BUG: Diagnostic contains:",
+            "    short s4 = Short.valueOf(Short.MIN_VALUE);",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    String boolStr = Boolean.valueOf(Boolean.FALSE).toString();",
+            "    int boolHash = Boolean.valueOf(false).hashCode();",
+            "    // BUG: Diagnostic contains:",
+            "    int byteHash = Byte.valueOf((Byte) Byte.MIN_VALUE).hashCode();",
+            "    String byteStr = Byte.valueOf(Byte.MIN_VALUE).toString();",
+            "",
+            "    String str1 = String.valueOf(0);",
+            "    // BUG: Diagnostic contains:",
+            "    String str2 = String.valueOf(\"1\");",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    ImmutableBiMap<Object, Object> o1 = ImmutableBiMap.copyOf(ImmutableBiMap.of());",
+            "    // BUG: Diagnostic contains:",
+            "    ImmutableList<Object> o2 = ImmutableList.copyOf(ImmutableList.of());",
+            "    ImmutableListMultimap<Object, Object> o3 =",
+            "        // BUG: Diagnostic contains:",
+            "        ImmutableListMultimap.copyOf(ImmutableListMultimap.of());",
+            "    // BUG: Diagnostic contains:",
+            "    ImmutableMap<Object, Object> o4 = ImmutableMap.copyOf(ImmutableMap.of());",
+            "    // BUG: Diagnostic contains:",
+            "    ImmutableMultimap<Object, Object> o5 = ImmutableMultimap.copyOf(ImmutableMultimap.of());",
+            "    // BUG: Diagnostic contains:",
+            "    ImmutableMultiset<Object> o6 = ImmutableMultiset.copyOf(ImmutableMultiset.of());",
+            "    // BUG: Diagnostic contains:",
+            "    ImmutableRangeMap<String, Object> o7 = ImmutableRangeMap.copyOf(ImmutableRangeMap.of());",
+            "    // BUG: Diagnostic contains:",
+            "    ImmutableRangeSet<String> o8 = ImmutableRangeSet.copyOf(ImmutableRangeSet.of());",
+            "    // BUG: Diagnostic contains:",
+            "    ImmutableSet<Object> o9 = ImmutableSet.copyOf(ImmutableSet.of());",
+            "    ImmutableSetMultimap<Object, Object> o10 =",
+            "        // BUG: Diagnostic contains:",
+            "        ImmutableSetMultimap.copyOf(ImmutableSetMultimap.of());",
+            "    // BUG: Diagnostic contains:",
+            "    ImmutableTable<Object, Object, Object> o11 = ImmutableTable.copyOf(ImmutableTable.of());",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  void replacement() {
+    BugCheckerRefactoringTestHelper.newInstance(
+            Assignment5DeleteIdentityConversion.class, getClass())
+        .addInputLines(
+            "A.java",
+            "import static com.google.errorprone.matchers.Matchers.staticMethod;",
+            "import static org.mockito.Mockito.when;",
+            "",
+            "import com.google.common.collect.ImmutableCollection;",
+            "import com.google.common.collect.ImmutableList;",
+            "import com.google.common.collect.ImmutableSet;",
+            "import java.util.ArrayList;",
+            "import java.util.Collection;",
+            "",
+            "public final class A {",
+            "  public void m() {",
+            "    ImmutableSet<Object> set1 = ImmutableSet.copyOf(ImmutableSet.of());",
+            "    ImmutableSet<Object> set2 = ImmutableSet.copyOf(ImmutableList.of());",
+            "",
+            "    ImmutableCollection<Integer> list1 = ImmutableList.copyOf(ImmutableList.of(1));",
+            "    ImmutableCollection<Integer> list2 = ImmutableList.copyOf(new ArrayList<>(ImmutableList.of(1)));",
+            "",
+            "    Collection<Integer> c1 = ImmutableSet.copyOf(ImmutableSet.of(1));",
+            "    Collection<Integer> c2 = ImmutableList.copyOf(new ArrayList<>(ImmutableList.of(1)));",
+            "",
+            "    Object o1 = ImmutableSet.copyOf(ImmutableList.of());",
+            "    Object o2 = ImmutableSet.copyOf(ImmutableSet.of());",
+            "",
+            "    when(\"foo\".contains(\"f\")).thenAnswer(inv -> ImmutableSet.copyOf(ImmutableList.of(1)));",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "import static com.google.errorprone.matchers.Matchers.staticMethod;",
+            "import static org.mockito.Mockito.when;",
+            "",
+            "import com.google.common.collect.ImmutableCollection;",
+            "import com.google.common.collect.ImmutableList;",
+            "import com.google.common.collect.ImmutableSet;",
+            "import java.util.ArrayList;",
+            "import java.util.Collection;",
+            "",
+            "public final class A {",
+            "  public void m() {",
+            "    ImmutableSet<Object> set1 = ImmutableSet.of();",
+            "    ImmutableSet<Object> set2 = ImmutableSet.copyOf(ImmutableList.of());",
+            "",
+            "    ImmutableCollection<Integer> list1 = ImmutableList.of(1);",
+            "    ImmutableCollection<Integer> list2 = ImmutableList.copyOf(new ArrayList<>(ImmutableList.of(1)));",
+            "",
+            "    Collection<Integer> c1 = ImmutableSet.of(1);",
+            "    Collection<Integer> c2 = ImmutableList.copyOf(new ArrayList<>(ImmutableList.of(1)));",
+            "",
+            "    Object o1 = ImmutableSet.copyOf(ImmutableList.of());",
+            "    Object o2 = ImmutableSet.of();",
+            "",
+            "    when(\"foo\".contains(\"f\")).thenAnswer(inv -> ImmutableSet.copyOf(ImmutableList.of(1)));",
+            "  }",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+}

workshop/src/test/java/tech/picnic/errorprone/workshop/refasterrules/WorkshopRefasterRulesTest.java

@@ -0,0 +1,37 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+import tech.picnic.errorprone.refaster.test.RefasterRuleCollection;
+
+final class WorkshopRefasterRulesTest {
+  @Test
+  void validateExampleRuleCollection() {
+    RefasterRuleCollection.validate(WorkshopAssignment0Rules.class);
+  }
+
+  @Test
+  void validateFirstWorkshopAssignment() {
+    RefasterRuleCollection.validate(WorkshopAssignment1Rules.class);
+  }
+
+  @Test
+  void validateSecondWorkshopAssignment() {
+    RefasterRuleCollection.validate(WorkshopAssignment2Rules.class);
+  }
+
+  @Test
+  void validateThirdWorkshopAssignment() {
+    RefasterRuleCollection.validate(WorkshopAssignment3Rules.class);
+  }
+
+  @Test
+  void validateFourthWorkshopAssignment() {
+    RefasterRuleCollection.validate(WorkshopAssignment4Rules.class);
+  }
+
+  @Test
+  void validateFifthWorkshopAssignment() {
+    RefasterRuleCollection.validate(WorkshopAssignment5Rules.class);
+  }
+}

workshop/src/test/resources/tech/picnic/errorprone/workshop/refasterrules/WorkshopAssignment0RulesTestInput.java

@@ -0,0 +1,10 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
+
+final class WorkshopAssignment0RulesTest implements RefasterRuleCollectionTestCase {
+  boolean testExampleStringIsEmpty() {
+    boolean b = "foo".length() == 0;
+    return "bar".length() == 0;
+  }
+}

workshop/src/test/resources/tech/picnic/errorprone/workshop/refasterrules/WorkshopAssignment0RulesTestOutput.java

@@ -0,0 +1,10 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
+
+final class WorkshopAssignment0RulesTest implements RefasterRuleCollectionTestCase {
+  boolean testExampleStringIsEmpty() {
+    boolean b = "foo".isEmpty();
+    return "bar".isEmpty();
+  }
+}

workshop/src/test/resources/tech/picnic/errorprone/workshop/refasterrules/WorkshopAssignment1RulesTestInput.java

@@ -0,0 +1,11 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
+
+final class WorkshopAssignment1RulesTest implements RefasterRuleCollectionTestCase {
+  String testNewStringCharArray() {
+    String.copyValueOf(new char[] {});
+    String.copyValueOf(new char[] {'f', 'o', 'o'});
+    return String.copyValueOf(new char[] {'b', 'a', 'r'});
+  }
+}

workshop/src/test/resources/tech/picnic/errorprone/workshop/refasterrules/WorkshopAssignment1RulesTestOutput.java

@@ -0,0 +1,11 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
+
+final class WorkshopAssignment1RulesTest implements RefasterRuleCollectionTestCase {
+  String testNewStringCharArray() {
+    new String(new char[] {});
+    new String(new char[] {'f', 'o', 'o'});
+    return new String(new char[] {'b', 'a', 'r'});
+  }
+}

workshop/src/test/resources/tech/picnic/errorprone/workshop/refasterrules/WorkshopAssignment2RulesTestInput.java

@@ -0,0 +1,20 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+import com.google.common.collect.ImmutableSet;
+import java.util.Collections;
+import java.util.List;
+import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
+
+final class WorkshopAssignment2RulesTest implements RefasterRuleCollectionTestCase {
+  @Override
+  public ImmutableSet<Object> elidedTypesAndStaticImports() {
+    return ImmutableSet.of(Collections.class);
+  }
+
+  List<Object> testImmutableListOfOne() {
+    Collections.singletonList(1);
+    Collections.singletonList("foo");
+    List.of(1);
+    return List.of("bar");
+  }
+}

workshop/src/test/resources/tech/picnic/errorprone/workshop/refasterrules/WorkshopAssignment2RulesTestOutput.java

@@ -0,0 +1,21 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
+import java.util.Collections;
+import java.util.List;
+import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
+
+final class WorkshopAssignment2RulesTest implements RefasterRuleCollectionTestCase {
+  @Override
+  public ImmutableSet<Object> elidedTypesAndStaticImports() {
+    return ImmutableSet.of(Collections.class);
+  }
+
+  List<Object> testImmutableListOfOne() {
+    ImmutableList.of(1);
+    ImmutableList.of("foo");
+    ImmutableList.of(1);
+    return ImmutableList.of("bar");
+  }
+}

workshop/src/test/resources/tech/picnic/errorprone/workshop/refasterrules/WorkshopAssignment3RulesTestInput.java

@@ -0,0 +1,24 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
+
+final class WorkshopAssignment3RulesTest implements RefasterRuleCollectionTestCase {
+  void testCheckArgumentWithoutMessage() {
+    if (!"foo".isEmpty()) {
+      throw new IllegalArgumentException();
+    }
+    if (!"bar".isEmpty()) {
+      throw new IllegalArgumentException();
+    }
+  }
+
+  void testCheckArgumentWithMessage() {
+    if (!"foo".isEmpty()) {
+      throw new IllegalArgumentException("The string is not empty");
+    }
+    if (!"bar".isEmpty()) {
+      throw new IllegalArgumentException(
+          "The rule should be able rewrite all kinds of messages ;).");
+    }
+  }
+}

workshop/src/test/resources/tech/picnic/errorprone/workshop/refasterrules/WorkshopAssignment3RulesTestOutput.java

@@ -0,0 +1,17 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+import static com.google.common.base.Preconditions.checkArgument;
+
+import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
+
+final class WorkshopAssignment3RulesTest implements RefasterRuleCollectionTestCase {
+  void testCheckArgumentWithoutMessage() {
+    checkArgument("foo".isEmpty());
+    checkArgument("bar".isEmpty());
+  }
+
+  void testCheckArgumentWithMessage() {
+    checkArgument("foo".isEmpty(), "The string is not empty");
+    checkArgument("bar".isEmpty(), "The rule should be able rewrite all kinds of messages ;).");
+  }
+}

workshop/src/test/resources/tech/picnic/errorprone/workshop/refasterrules/WorkshopAssignment4RulesTestInput.java

@@ -0,0 +1,25 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+import com.google.common.collect.ImmutableSet;
+import java.math.RoundingMode;
+import java.util.Objects;
+import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
+
+final class WorkshopAssignment4RulesTest implements RefasterRuleCollectionTestCase {
+  @Override
+  public ImmutableSet<Object> elidedTypesAndStaticImports() {
+    return ImmutableSet.of(Objects.class);
+  }
+
+  ImmutableSet<Boolean> testPrimitiveOrReferenceEqualityEnum() {
+    // Don't pay attention to the `ImmutableSet#of` here, it's just syntactical sugar for the
+    // testing framework.
+    return ImmutableSet.of(
+        "foo".equals("bar"),
+        Integer.valueOf(1).equals(2),
+        RoundingMode.UP.equals(RoundingMode.DOWN),
+        Objects.equals(RoundingMode.UP, RoundingMode.DOWN),
+        !RoundingMode.UP.equals(RoundingMode.DOWN),
+        !Objects.equals(RoundingMode.UP, RoundingMode.DOWN));
+  }
+}

workshop/src/test/resources/tech/picnic/errorprone/workshop/refasterrules/WorkshopAssignment4RulesTestOutput.java

@@ -0,0 +1,25 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+import com.google.common.collect.ImmutableSet;
+import java.math.RoundingMode;
+import java.util.Objects;
+import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
+
+final class WorkshopAssignment4RulesTest implements RefasterRuleCollectionTestCase {
+  @Override
+  public ImmutableSet<Object> elidedTypesAndStaticImports() {
+    return ImmutableSet.of(Objects.class);
+  }
+
+  ImmutableSet<Boolean> testPrimitiveOrReferenceEqualityEnum() {
+    // Don't pay attention to the `ImmutableSet#of` here, it's just syntactical sugar for the
+    // testing framework.
+    return ImmutableSet.of(
+        "foo".equals("bar"),
+        Integer.valueOf(1).equals(2),
+        RoundingMode.UP == RoundingMode.DOWN,
+        RoundingMode.UP == RoundingMode.DOWN,
+        RoundingMode.UP != RoundingMode.DOWN,
+        RoundingMode.UP != RoundingMode.DOWN);
+  }
+}

workshop/src/test/resources/tech/picnic/errorprone/workshop/refasterrules/WorkshopAssignment5RulesTestInput.java

@@ -0,0 +1,11 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+import java.util.stream.Stream;
+import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
+
+final class WorkshopAssignment5RulesTest implements RefasterRuleCollectionTestCase {
+  boolean testStreamDoAllMatch() {
+    boolean example = Stream.of("foo").noneMatch(s -> !s.isBlank());
+    return Stream.of("bar").noneMatch(b -> !b.startsWith("b"));
+  }
+}

workshop/src/test/resources/tech/picnic/errorprone/workshop/refasterrules/WorkshopAssignment5RulesTestOutput.java

@@ -0,0 +1,11 @@
+package tech.picnic.errorprone.workshop.refasterrules;
+
+import java.util.stream.Stream;
+import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
+
+final class WorkshopAssignment5RulesTest implements RefasterRuleCollectionTestCase {
+  boolean testStreamDoAllMatch() {
+    boolean example = Stream.of("foo").allMatch(s -> s.isBlank());
+    return Stream.of("bar").allMatch(b -> b.startsWith("b"));
+  }
+}