GH-116 - PublishedEvents now sees events from asynchronous event listeners as well.

The ApplicationListener we deploy to capture events published  during a test method execution now uses an InheritableThreadLocal so that events published on threads spawned from the main test execution thread also end up in the PublishedEvents instance prepared for the test method.

Also, the registration of that particular event listener avoids duplicate registrations by inspecting the application context in use for the test method execution for an already registered listener, falling back to registering one.

spring-modulith-test/src/test/java/example/AsyncEventListener.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2023 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 example;
+
+import lombok.RequiredArgsConstructor;
+
+import org.springframework.context.ApplicationEventPublisher;
+import org.springframework.context.event.EventListener;
+import org.springframework.scheduling.annotation.Async;
+import org.springframework.stereotype.Component;
+
+@Component
+@RequiredArgsConstructor
+public class AsyncEventListener {
+
+	private final ApplicationEventPublisher publisher;
+
+	@Async
+	@EventListener
+	void on(FirstEvent event) {
+		publisher.publishEvent(new SecondEvent());
+	}
+
+	@Async
+	@EventListener
+	void on(SecondEvent event) {
+		publisher.publishEvent(new ThirdEvent());
+	}
+
+	public static record FirstEvent() {}
+
+	static record SecondEvent() {}
+
+	public static record ThirdEvent() {}
+}

spring-modulith-test/src/test/java/example/TestConfiguration.java

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2023 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 example;
+
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.scheduling.annotation.EnableAsync;
+
+@EnableAsync(proxyTargetClass = true)
+@SpringBootApplication
+public class TestConfiguration {}