Emit warning when @SuiteDisplayName is used with a blank string

Resolves #4810.

Author: raccoonback

junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/SuiteTestDescriptor.java

@@ -80,7 +80,7 @@ final class SuiteTestDescriptor extends AbstractTestDescriptor {
 	SuiteTestDescriptor(UniqueId id, Class<?> suiteClass, ConfigurationParameters configurationParameters,
 			OutputDirectoryProvider outputDirectoryProvider, EngineDiscoveryListener discoveryListener,
 			DiscoveryIssueReporter issueReporter) {
-		super(id, getSuiteDisplayName(suiteClass), ClassSource.from(suiteClass));
+		super(id, getSuiteDisplayName(suiteClass, issueReporter), ClassSource.from(suiteClass));
 		this.configurationParameters = configurationParameters;
 		this.outputDirectoryProvider = outputDirectoryProvider;
 		this.failIfNoTests = getFailIfNoTests(suiteClass);
@@ -140,12 +140,20 @@ public Type getType() {
 		return Type.CONTAINER;
 	}
 
-	private static String getSuiteDisplayName(Class<?> testClass) {
+	private static String getSuiteDisplayName(Class<?> suiteClass, DiscoveryIssueReporter issueReporter) {
 		// @formatter:off
-		return findAnnotation(testClass, SuiteDisplayName.class)
+		var nonBlank = issueReporter.createReportingCondition(StringUtils::isNotBlank, __ -> {
+			String message = "@SuiteDisplayName on %s must be declared with a non-blank value.".formatted(
+					suiteClass.getName());
+			return DiscoveryIssue.builder(DiscoveryIssue.Severity.WARNING, message)
+					.source(ClassSource.from(suiteClass))
+					.build();
+		}).toPredicate();
+
+		return findAnnotation(suiteClass, SuiteDisplayName.class)
 				.map(SuiteDisplayName::value)
-				.filter(StringUtils::isNotBlank)
-				.orElse(testClass.getSimpleName());
+				.filter(nonBlank)
+				.orElse(suiteClass.getSimpleName());
 		// @formatter:on
 	}
 

platform-tests/src/test/java/org/junit/platform/suite/engine/SuiteEngineTests.java

@@ -68,6 +68,7 @@
 import org.junit.platform.suite.engine.testcases.SingleTestTestCase;
 import org.junit.platform.suite.engine.testcases.TaggedTestTestCase;
 import org.junit.platform.suite.engine.testsuites.AbstractSuite;
+import org.junit.platform.suite.engine.testsuites.BlankSuiteDisplayNameSuite;
 import org.junit.platform.suite.engine.testsuites.ConfigurationSuite;
 import org.junit.platform.suite.engine.testsuites.CyclicSuite;
 import org.junit.platform.suite.engine.testsuites.DynamicSuite;
@@ -88,6 +89,7 @@
 import org.junit.platform.suite.engine.testsuites.SuiteSuite;
 import org.junit.platform.suite.engine.testsuites.SuiteWithErroneousTestSuite;
 import org.junit.platform.suite.engine.testsuites.ThreePartCyclicSuite;
+import org.junit.platform.suite.engine.testsuites.WhitespaceSuiteDisplayNameSuite;
 import org.junit.platform.testkit.engine.EngineTestKit;
 
 /**
@@ -705,6 +707,38 @@ void reportsChildrenOfEnginesInSuiteAsSkippedWhenCancelledDuringExecution() {
 		}
 	}
 
+	@Test
+	void blankSuiteDisplayNameGeneratesWarning() {
+		var expectedMessage = "@SuiteDisplayName on %s must be declared with a non-blank value.".formatted(
+			BlankSuiteDisplayNameSuite.class.getName());
+		var expectedIssue = DiscoveryIssue.builder(Severity.WARNING, expectedMessage).source(
+			ClassSource.from(BlankSuiteDisplayNameSuite.class)).build();
+
+		var testKit = EngineTestKit.engine(ENGINE_ID).selectors(selectClass(BlankSuiteDisplayNameSuite.class));
+
+		assertThat(testKit.discover().getDiscoveryIssues()).contains(expectedIssue);
+	}
+
+	@Test
+	void whitespaceSuiteDisplayNameGeneratesWarning() {
+		var expectedMessage = "@SuiteDisplayName on %s must be declared with a non-blank value.".formatted(
+			WhitespaceSuiteDisplayNameSuite.class.getName());
+		var expectedIssue = DiscoveryIssue.builder(Severity.WARNING, expectedMessage).source(
+			ClassSource.from(WhitespaceSuiteDisplayNameSuite.class)).build();
+
+		var testKit = EngineTestKit.engine(ENGINE_ID).selectors(selectClass(WhitespaceSuiteDisplayNameSuite.class));
+
+		assertThat(testKit.discover().getDiscoveryIssues()).contains(expectedIssue);
+	}
+
+	@Test
+	void validSuiteDisplayNameGeneratesNoWarning() {
+		var testKit = EngineTestKit.engine(ENGINE_ID).selectors(selectClass(SuiteDisplayNameSuite.class));
+
+		assertThat(testKit.discover().getDiscoveryIssues()) //
+				.noneMatch(issue -> issue.message().contains("@SuiteDisplayName"));
+	}
+
 	// -----------------------------------------------------------------------------------------------------------------
 
 	static class CancellingSuite extends SelectClassesSuite {

platform-tests/src/test/java/org/junit/platform/suite/engine/testsuites/BlankSuiteDisplayNameSuite.java

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.platform.suite.engine.testsuites;
+
+import org.junit.platform.suite.api.SelectClasses;
+import org.junit.platform.suite.api.Suite;
+import org.junit.platform.suite.api.SuiteDisplayName;
+import org.junit.platform.suite.engine.testcases.SingleTestTestCase;
+
+/**
+ * Test suite with blank @SuiteDisplayName to verify validation.
+ *
+ * @since 6.0
+ */
+@Suite
+@SelectClasses(SingleTestTestCase.class)
+@SuiteDisplayName("")
+public class BlankSuiteDisplayNameSuite {
+}

platform-tests/src/test/java/org/junit/platform/suite/engine/testsuites/WhitespaceSuiteDisplayNameSuite.java

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.platform.suite.engine.testsuites;
+
+import org.junit.platform.suite.api.SelectClasses;
+import org.junit.platform.suite.api.Suite;
+import org.junit.platform.suite.api.SuiteDisplayName;
+import org.junit.platform.suite.engine.testcases.SingleTestTestCase;
+
+/**
+ * Test suite with whitespace-only @SuiteDisplayName to verify validation.
+ *
+ * @since 6.0
+ */
+@Suite
+@SelectClasses(SingleTestTestCase.class)
+@SuiteDisplayName("   ")
+public class WhitespaceSuiteDisplayNameSuite {
+}