GH-216 - Forward an ApplicationContext's ExecutorService to Scenario instances by default.

We now register a default customizer on the Scenario instances created to pick up an ExecutorService defined in the ApplicationContext so that customizations made to that are considered in the test execution.

spring-modulith-test/src/main/java/org/springframework/modulith/test/ScenarioCustomizer.java

@@ -16,13 +16,17 @@
 package org.springframework.modulith.test;
 
 import java.lang.reflect.Method;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ExecutorService;
 import java.util.function.Function;
+import java.util.function.Supplier;
 
 import org.awaitility.core.ConditionFactory;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.InvocationInterceptor;
 import org.junit.jupiter.api.extension.ReflectiveInvocationContext;
 import org.springframework.context.ApplicationContext;
+import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
 import org.springframework.test.context.junit.jupiter.SpringExtension;
 import org.springframework.util.Assert;
 
@@ -43,6 +47,30 @@ public interface ScenarioCustomizer extends InvocationInterceptor {
 	 */
 	Function<ConditionFactory, ConditionFactory> getDefaultCustomizer(Method method, ApplicationContext context);
 
+	/**
+	 * Creates a default scenario customizer that will try to find an {@link ExecutorService} in the given
+	 * {@link ApplicationContext} in the following order:
+	 * <ol>
+	 * <li>A unique {@link ExecutorService} bean defined</li>
+	 * <li>A {@link ThreadPoolTaskExecutor} bean defined (the default Spring Boot creates in case no {@link Executor} is
+	 * explicitly defined in the {@link ApplicationContext}</li>
+	 * </ol>
+	 *
+	 * @param context must not be {@literal null}.
+	 * @return will never be {@literal null}.
+	 */
+	public static Function<ConditionFactory, ConditionFactory> forwardExecutorService(ApplicationContext context) {
+
+		Supplier<ExecutorService> fallback = () -> {
+			var executor = context.getBeanProvider(ThreadPoolTaskExecutor.class).getIfUnique();
+			return executor == null ? null : executor.getThreadPoolExecutor();
+		};
+
+		var executorService = context.getBeanProvider(ExecutorService.class).getIfUnique(fallback);
+
+		return executorService != null ? it -> it.pollExecutorService(executorService) : Function.identity();
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.junit.jupiter.api.extension.InvocationInterceptor#interceptTestTemplateMethod(org.junit.jupiter.api.extension.InvocationInterceptor.Invocation, org.junit.jupiter.api.extension.ReflectiveInvocationContext, org.junit.jupiter.api.extension.ExtensionContext)

spring-modulith-test/src/main/java/org/springframework/modulith/test/ScenarioParameterResolver.java

@@ -77,7 +77,8 @@ class ScenarioParameterResolver implements ParameterResolver, AfterEachCallback
 		var operations = resolveTransactionTemplate(context);
 		var events = (AssertablePublishedEvents) delegate.resolveParameter(parameterContext, extensionContext);
 
-		return new Scenario(operations, context, events);
+		return new Scenario(operations, context, events)
+				.setDefaultCustomizer(ScenarioCustomizer.forwardExecutorService(context));
 	}
 
 	private TransactionTemplate resolveTransactionTemplate(ApplicationContext context) {

spring-modulith-test/src/test/java/org/springframework/modulith/test/ScenarioCustomizerIntegrationTests.java

@@ -19,12 +19,17 @@ import static org.assertj.core.api.Assertions.*;
 import static org.mockito.Mockito.*;
 
 import java.lang.reflect.Method;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 import java.util.function.Function;
 
+import org.awaitility.Awaitility;
 import org.awaitility.core.ConditionFactory;
+import org.awaitility.core.ExecutorLifecycle;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
@@ -50,8 +55,15 @@ class ScenarioCustomizerIntegrationTests {
 		TransactionTemplate transactionTemplate() {
 			return mock(TransactionTemplate.class);
 		}
+
+		@Bean
+		ExecutorService executorService() {
+			return Executors.newSingleThreadExecutor();
+		}
 	}
 
+	@Autowired ExecutorService executorService;
+
 	@BeforeEach
 	void setUp() {
 		TestScenarioCustomizer.invoked = false;
@@ -61,6 +73,8 @@ class ScenarioCustomizerIntegrationTests {
 	void customizerGetsAppliedForScenarioParameter(Scenario scenario) {
 
 		assertThat(TestScenarioCustomizer.invoked).isTrue();
+		assertThat(TestScenarioCustomizer.SAMPLE).isNotNull();
+
 		assertThat(ReflectionTestUtils.getField(scenario, "defaultCustomizer"))
 				.isSameAs(TestScenarioCustomizer.SAMPLE);
 	}
@@ -70,9 +84,23 @@ class ScenarioCustomizerIntegrationTests {
 		assertThat(TestScenarioCustomizer.invoked).isFalse();
 	}
 
+	@Test // GH-165
+	@SuppressWarnings("unchecked")
+	void forwardsExecutorServiceFromApplicationContext(Scenario scenario) {
+
+		var customizer = (Function<ConditionFactory, ConditionFactory>) ReflectionTestUtils.getField(scenario,
+				"defaultCustomizer");
+
+		var factory = customizer.apply(Awaitility.await());
+		var lifecycle = (ExecutorLifecycle) ReflectionTestUtils.getField(factory, "executorLifecycle");
+
+		assertThat(lifecycle).isNotNull();
+		assertThat(lifecycle.supplyExecutorService()).isEqualTo(executorService);
+	}
+
 	static class TestScenarioCustomizer implements ScenarioCustomizer {
 
-		static Function<ConditionFactory, ConditionFactory> SAMPLE = it -> it;
+		static Function<ConditionFactory, ConditionFactory> SAMPLE;
 		static boolean invoked = false;
 
 		@Override
@@ -81,6 +109,8 @@ class ScenarioCustomizerIntegrationTests {
 
 			invoked = true;
 
+			SAMPLE = ScenarioCustomizer.forwardExecutorService(context);
+
 			return SAMPLE;
 		}
 	}