Add ExceptionEvent

An exception event wraps an event that caused an exception inside of an
event handler while being dispatched and is then dispatched to dedicated
handlers.

event-bus-core/src/test/java/dev/kske/eventbus/core/DeadTest.java

@@ -31,7 +31,7 @@ class DeadTest {
 
 	/**
 	 * Tests how the event bus reacts to an unhandled dead event. This should not lead to an
-	 * exception or endless recursion and instead be logged.
+	 * exception or an endless recursion and should be logged instead.
 	 * 
 	 * @since 1.1.0
 	 */

event-bus-core/src/test/java/dev/kske/eventbus/core/ExceptionTest.java

@@ -0,0 +1,62 @@
+package dev.kske.eventbus.core;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests the dispatching of an exception event if an event handler threw an exception.
+ * 
+ * @author Kai S. K. Engelbart
+ * @since 1.1.0
+ */
+class ExceptionTest {
+
+	EventBus			bus			= new EventBus();
+	String				event		= "This event will cause an exception";
+	RuntimeException	exception	= new RuntimeException("I failed");
+	boolean				exceptionEventHandled;
+
+	/**
+	 * Tests exception event delivery.
+	 * 
+	 * @since 1.1.0
+	 */
+	@Test
+	void testExceptionEvent() {
+		bus.registerListener(this);
+		bus.registerListener(new ExceptionListener());
+		bus.dispatch(event);
+		assertTrue(exceptionEventHandled);
+		bus.clearListeners();
+	}
+
+	/**
+	 * Tests how the event bus reacts to an unhandled exception event. This should not lead to an
+	 * exception or an endless recursion and should be logged instead.
+	 * 
+	 * @since 1.1.0
+	 */
+	@Test
+	void testUnhandledExceptionEvent() {
+		bus.registerListener(this);
+		bus.dispatch(event);
+		bus.removeListener(this);
+	}
+
+	@Event(String.class)
+	void onString() {
+		throw exception;
+	}
+
+	class ExceptionListener {
+
+		@Event
+		void onExceptionEvent(ExceptionEvent exceptionEvent) {
+			assertEquals(bus, exceptionEvent.getEventBus());
+			assertEquals(event, exceptionEvent.getEvent());
+			assertEquals(exception, exceptionEvent.getCause());
+			exceptionEventHandled = true;
+		}
+	}
+}