Why doesn't this match?

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/AssortedRules.java

@@ -23,6 +23,7 @@ import java.util.HashSet;
 import java.util.Iterator;
 import java.util.Objects;
 import java.util.Set;
+import java.util.function.Supplier;
 import java.util.stream.Stream;
 import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
@@ -35,6 +36,18 @@ import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 final class AssortedRules {
   private AssortedRules() {}
 
+  final class IllegalStateExceptionSupplier {
+    @BeforeTemplate
+    Supplier<IllegalStateException> before(String message) {
+      return () -> new IllegalStateException(message);
+    }
+
+    @AfterTemplate
+    Supplier<IllegalStateException> after(String message) {
+      return () -> new IllegalStateException("XXX");
+    }
+  }
+
   /** Prefer {@link Objects#checkIndex(int, int)} over the Guava alternative. */
   static final class CheckIndex {
     @BeforeTemplate

error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/AssortedRulesTestInput.java

@@ -13,6 +13,7 @@ import com.google.common.collect.Streams;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.stream.Stream;
+import reactor.core.publisher.Mono;
 import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
 
 final class AssortedRulesTest implements RefasterRuleCollectionTestCase {
@@ -28,6 +29,10 @@ final class AssortedRulesTest implements RefasterRuleCollectionTestCase {
         toImmutableSet());
   }
 
+  Mono<Void> testIllegalStateExceptionSupplier() {
+    return Mono.error(() -> new IllegalStateException("ISE"));
+  }
+
   int testCheckIndex() {
     return Preconditions.checkElementIndex(0, 1);
   }