Improve error message for non-inner @Nested classes

Author: marcphilipp

junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/predicates/TestClassPredicates.java

@@ -15,6 +15,7 @@
 import static org.junit.platform.commons.support.ModifierSupport.isAbstract;
 import static org.junit.platform.commons.support.ModifierSupport.isNotAbstract;
 import static org.junit.platform.commons.support.ModifierSupport.isNotPrivate;
+import static org.junit.platform.commons.util.ReflectionUtils.isInnerClass;
 import static org.junit.platform.commons.util.ReflectionUtils.isMethodPresent;
 import static org.junit.platform.commons.util.ReflectionUtils.isNestedClassPresent;
 
@@ -99,12 +100,16 @@ private static Condition<Class<?>> isNotLocal(DiscoveryIssueReporter issueReport
 	}
 
 	private static Condition<Class<?>> isInner(DiscoveryIssueReporter issueReporter) {
-		return issueReporter.createReportingCondition(ReflectionUtils::isInnerClass,
-			testClass -> createIssue("@Nested", testClass, "must be an inner class but is static"));
+		return issueReporter.createReportingCondition(ReflectionUtils::isInnerClass, testClass -> {
+			if (testClass.getEnclosingClass() == null) {
+				return createIssue("@Nested", testClass, "must not be a top-level class");
+			}
+			return createIssue("@Nested", testClass, "must not be static");
+		});
 	}
 
 	private static Condition<Class<?>> isNotInner(DiscoveryIssueReporter issueReporter) {
-		return issueReporter.createReportingCondition(testClass -> !ReflectionUtils.isInnerClass(testClass),
+		return issueReporter.createReportingCondition(testClass -> !isInnerClass(testClass),
 			testClass -> createIssue("Test", testClass, "must not be an inner class unless annotated with @Nested"));
 	}
 

jupiter-tests/src/test/java/org/junit/jupiter/engine/discovery/DiscoveryTests.java

@@ -249,10 +249,10 @@ void reportsWarningForInvalidNestedTestClass(LauncherDiscoveryRequest request) {
 		var discoveryIssues = results.getDiscoveryIssues().stream().sorted(comparing(DiscoveryIssue::message)).toList();
 		assertThat(discoveryIssues).hasSize(2);
 		assertThat(discoveryIssues.getFirst().message()) //
-				.isEqualTo("@Nested class '%s' must be an inner class but is static. It will not be executed.",
+				.isEqualTo("@Nested class '%s' must not be private. It will not be executed.",
 					InvalidTestCases.InvalidTestClassTestCase.Inner.class.getName());
 		assertThat(discoveryIssues.getLast().message()) //
-				.isEqualTo("@Nested class '%s' must not be private. It will not be executed.",
+				.isEqualTo("@Nested class '%s' must not be static. It will not be executed.",
 					InvalidTestCases.InvalidTestClassTestCase.Inner.class.getName());
 	}
 

jupiter-tests/src/test/java/org/junit/jupiter/engine/discovery/predicates/TestClassPredicatesTests.java

@@ -254,7 +254,21 @@ void staticNestedClassEvaluatesToFalse() {
 			assertThat(predicates.isAnnotatedWithNestedAndValid).rejects(candidate);
 
 			var issue = DiscoveryIssue.builder(Severity.WARNING,
-				"@Nested class '%s' must be an inner class but is static. It will not be executed.".formatted(
+				"@Nested class '%s' must not be static. It will not be executed.".formatted(candidate.getName())) //
+					.source(ClassSource.from(candidate)) //
+					.build();
+			assertThat(discoveryIssues.stream().distinct()).containsExactly(issue);
+		}
+
+		@Test
+		void topLevelClassEvaluatesToFalse() {
+			var candidate = InvalidTopLevelNestedTestClass.class;
+			assertThat(predicates.isAnnotatedWithNested).accepts(candidate);
+			assertFalse(predicates.isValidNestedTestClass(candidate));
+			assertThat(predicates.isAnnotatedWithNestedAndValid).rejects(candidate);
+
+			var issue = DiscoveryIssue.builder(Severity.WARNING,
+				"@Nested class '%s' must not be a top-level class. It will not be executed.".formatted(
 					candidate.getName())) //
 					.source(ClassSource.from(candidate)) //
 					.build();
@@ -298,8 +312,7 @@ class LocalClass {
 			assertThat(predicates.isAnnotatedWithNestedAndValid).rejects(candidate);
 
 			var issue = DiscoveryIssue.builder(Severity.WARNING,
-				"@Nested class '%s' must be an inner class but is static. It will not be executed.".formatted(
-					candidate.getName())) //
+				"@Nested class '%s' must not be static. It will not be executed.".formatted(candidate.getName())) //
 					.source(ClassSource.from(candidate)) //
 					.build();
 			assertThat(discoveryIssues.stream().distinct()).containsExactly(issue);
@@ -469,3 +482,11 @@ void second() {
 
 	}
 }
+
+@SuppressWarnings("NewClassNamingConvention")
+@Nested
+class InvalidTopLevelNestedTestClass {
+	@Test
+	void test() {
+	}
+}