Add TestMethodsShouldBeVoid recipe to fix tests not discovered

src/main/java/org/openrewrite/java/testing/cleanup/TestMethodsShouldBeVoid.java

@@ -0,0 +1,115 @@
+/*
+ * Copyright 2025 the original author or authors.
+ * <p>
+ * Licensed under the Moderne Source Available License (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * <p>
+ * https://docs.moderne.io/licensing/moderne-source-available-license
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.openrewrite.java.testing.cleanup;
+
+import org.jspecify.annotations.Nullable;
+import org.openrewrite.ExecutionContext;
+import org.openrewrite.Recipe;
+import org.openrewrite.TreeVisitor;
+import org.openrewrite.java.JavaIsoVisitor;
+import org.openrewrite.java.JavaVisitor;
+import org.openrewrite.java.tree.J;
+import org.openrewrite.java.tree.JavaType;
+import org.openrewrite.java.tree.Statement;
+import org.openrewrite.java.tree.TypeUtils;
+
+import static java.util.Objects.requireNonNull;
+
+public class TestMethodsShouldBeVoid extends Recipe {
+
+    @Override
+    public String getDisplayName() {
+        return "Test methods should have void return type";
+    }
+
+    @Override
+    public String getDescription() {
+        return "Test methods annotated with `@Test`, `@ParameterizedTest`, `@RepeatedTest`, `@TestTemplate` " +
+                "should have `void` return type. Non-void return types can cause test discovery issues, " +
+                "and warnings as of JUnit 5.13+. This recipe changes the return type to `void` and removes `return` statements.";
+    }
+
+    @Override
+    public TreeVisitor<?, ExecutionContext> getVisitor() {
+        return new JavaIsoVisitor<ExecutionContext>() {
+            @Override
+            public J.MethodDeclaration visitMethodDeclaration(J.MethodDeclaration method, ExecutionContext ctx) {
+                J.MethodDeclaration m = super.visitMethodDeclaration(method, ctx);
+
+                // Check if method has a test annotation & body
+                if (!hasTestAnnotation(m) || m.getBody() == null) {
+                    return m;
+                }
+
+                // Check if return type is already void
+                JavaType.Primitive voidType = JavaType.Primitive.Void;
+                if (m.getReturnTypeExpression() == null || TypeUtils.isOfType(m.getReturnTypeExpression().getType(), voidType)) {
+                    return m;
+                }
+
+                // Change return type to void
+                m = m.withReturnTypeExpression(new J.Primitive(
+                        m.getReturnTypeExpression().getId(),
+                        m.getReturnTypeExpression().getPrefix(),
+                        m.getReturnTypeExpression().getMarkers(),
+                        JavaType.Primitive.Void
+                ));
+
+                // Update method type
+                if (m.getMethodType() != null) {
+                    m = m.withMethodType(m.getMethodType().withReturnType(voidType));
+                }
+
+                // Remove return statements that are not in nested classes or lambdas
+                return m.withBody((J.Block) new RemoveDirectReturns().visitBlock(requireNonNull(m.getBody()), ctx));
+            }
+
+            private boolean hasTestAnnotation(J.MethodDeclaration method) {
+                for (J.Annotation annotation : method.getLeadingAnnotations()) {
+                    if (TypeUtils.isOfClassType(annotation.getType(), "org.junit.Test") ||
+                            TypeUtils.isOfClassType(annotation.getType(), "org.junit.jupiter.api.RepeatedTest") ||
+                            TypeUtils.isOfClassType(annotation.getType(), "org.junit.jupiter.api.Test") ||
+                            TypeUtils.isOfClassType(annotation.getType(), "org.junit.jupiter.api.TestTemplate") ||
+                            TypeUtils.isOfClassType(annotation.getType(), "org.junit.jupiter.params.ParameterizedTest")) {
+                        return true;
+                    }
+                }
+                return false;
+            }
+        };
+    }
+
+    private static class RemoveDirectReturns extends JavaVisitor<ExecutionContext> {
+        @Override
+        public J visitLambda(J.Lambda lambda, ExecutionContext ctx) {
+            return lambda; // Retain nested returns
+        }
+
+        @Override
+        public J visitNewClass(J.NewClass newClass, ExecutionContext ctx) {
+            return newClass; // Retain nested returns
+        }
+
+        @Override
+        public @Nullable J visitReturn(J.Return retrn, ExecutionContext ctx) {
+            return retrn.getExpression() instanceof Statement ?
+                    // Retain any side effects from expressions in return statements
+                    retrn.getExpression().withPrefix(retrn.getPrefix()) :
+                    // Remove any other return statements
+                    null;
+        }
+    }
+}

src/main/resources/META-INF/rewrite/examples.yml

@@ -1344,6 +1344,32 @@ examples:
     language: java
 ---
 type: specs.openrewrite.org/v1beta/example
+recipeName: org.openrewrite.java.testing.cleanup.TestMethodsShouldBeVoid
+examples:
+- description: ''
+  sources:
+  - before: |
+      import org.junit.jupiter.api.Test;
+
+      class ATest {
+          @Test
+          int testMethod() {
+              int i = 42;
+              return i;
+          }
+      }
+    after: |
+      import org.junit.jupiter.api.Test;
+
+      class ATest {
+          @Test
+          void testMethod() {
+              int i = 42;
+          }
+      }
+    language: java
+---
+type: specs.openrewrite.org/v1beta/example
 recipeName: org.openrewrite.java.testing.datafaker.JavaFakerToDataFaker
 examples:
 - description: ''

src/main/resources/META-INF/rewrite/junit5.yml

@@ -32,6 +32,7 @@ recipeList:
   - org.openrewrite.java.testing.cleanup.RemoveTestPrefix
   - org.openrewrite.java.testing.cleanup.SimplifyTestThrows
   - org.openrewrite.java.testing.cleanup.TestsShouldNotBePublic
+  - org.openrewrite.java.testing.cleanup.TestMethodsShouldBeVoid
   - org.openrewrite.java.testing.junit5.AddParameterizedTestAnnotation
   - org.openrewrite.java.testing.junit5.RemoveDuplicateTestTemplates
   - org.openrewrite.java.testing.junit5.RemoveTryCatchFailBlocks