GH-1395 - Fall back to enabled tests for multiple main classes present.

Author: odrotbohm

spring-modulith-junit/src/main/java/org/springframework/modulith/junit/TestExecutionCondition.java

@@ -24,6 +24,7 @@
 import org.slf4j.LoggerFactory;
 import org.springframework.boot.SpringBootConfiguration;
 import org.springframework.boot.test.context.AnnotatedClassFinder;
+import org.springframework.lang.Nullable;
 import org.springframework.modulith.core.ApplicationModule;
 import org.springframework.modulith.core.ApplicationModuleDependencies;
 import org.springframework.modulith.core.ApplicationModules;
@@ -71,7 +72,7 @@ ConditionEvaluationResult evaluate(ConditionContext context) {
 			return enabled("Change in test class detected, executing test.");
 		}
 
-		var mainClass = SPA_CLASS_FINDER.findFromClass(testClass);
+		var mainClass = findMainClass(testClass);
 
 		if (mainClass == null) {// TODO:: Try with @ApplicationModuleTest -> main class
 			return enabled("Unable to locate SpringBootApplication Class");
@@ -122,5 +123,19 @@ private static ConditionEvaluationResult result(Function<String, ConditionEvalua
 		return creator.apply(message);
 	}
 
+	/**
+	 * Finds the canonical main class of the application. Falls back to {@literal null} in case multiple types are found.
+	 *
+	 * @param testClass must not be {@literal null}.
+	 */
+	private static @Nullable Class<?> findMainClass(Class<?> testClass) {
+
+		try {
+			return SPA_CLASS_FINDER.findFromClass(testClass);
+		} catch (IllegalStateException o_O) {
+			return null;
+		}
+	}
+
 	record ConditionContext(Class<?> testClass, Changes changes) {}
 }

spring-modulith-junit/src/test/java/org/springframework/modulith/junit/TestExecutionConditionUnitTests.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * 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.springframework.modulith.junit;
+
+import static org.assertj.core.api.Assertions.*;
+
+import java.util.stream.Stream;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.SpringBootConfiguration;
+import org.springframework.modulith.junit.diff.ModifiedFile;
+
+/**
+ * Unit tests for {@link TestExecutionCondition}.
+ *
+ * @author Oliver Drotbohm
+ */
+class TestExecutionConditionUnitTests {
+
+	@Test // GH-1391
+	void fallsBackToEnabledTestIfMultipleMainClassesFound() {
+
+		var changes = Changes.of(Stream.of(new ModifiedFile("Foo.java")));
+		var ctx = new TestExecutionCondition.ConditionContext(getClass(), changes);
+
+		assertThat(new TestExecutionCondition().evaluate(ctx).isDisabled()).isFalse();
+	}
+
+	@SpringBootConfiguration
+	static class First {}
+
+	@SpringBootConfiguration
+	static class Second {}
+}