Add simple unit test and fix event handler ordering

src/main/java/dev/kske/eventbus/EventBus.java

@@ -76,7 +76,7 @@ public final class EventBus {
 			@SuppressWarnings("unchecked")
 			var realParam = (Class<? extends IEvent>) param;
 			if (!bindings.containsKey(realParam))
-				bindings.put(realParam, new HashSet<>());
+				bindings.put(realParam, new TreeSet<>());
 
 			bindings.get(realParam).add(new EventHandler(listener, method, annotation));
 		}

src/main/java/dev/kske/eventbus/EventHandler.java

@@ -32,12 +32,14 @@ final class EventHandler implements Comparable<EventHandler> {
 	/**
 	 * Compares this to another event handler based on {@link Event#priority()}. In case of equal
 	 * priority a non-zero value based on hash codes is returned.
+	 * <p>
+	 * This is used to retrieve event handlers in the correct order from a tree set.
 	 *
 	 * @since 0.0.1
 	 */
 	@Override
 	public int compareTo(EventHandler other) {
-		int priority = annotation.priority() - other.annotation.priority();
+		int priority = other.annotation.priority() - annotation.priority();
 		if (priority == 0)
 			priority = listener.hashCode() - other.listener.hashCode();
 		return priority == 0 ? hashCode() - other.hashCode() : priority;

src/test/java/dev/kske/eventbus/EventBusTest.java

@@ -0,0 +1,39 @@
+package dev.kske.eventbus;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.*;
+
+/**
+ * Tests the of the event bus library.
+ *
+ * @author Kai S. K. Engelbart
+ * @since 0.0.1
+ */
+class EventBusTest implements EventListener {
+
+	public EventBus eventBus = new EventBus();
+	int hits;
+
+	@BeforeEach
+	public void registerListener() {
+		eventBus.registerListener(this);
+	}
+
+	@Test
+	void testDispatch() {
+		eventBus.dispatch(new SimpleEvent());
+	}
+
+	@Event(priority = 50)
+	public void onSimpleEventSecond(SimpleEvent event) {
+		++hits;
+		assertEquals(2, hits);
+	}
+
+	@Event(priority = 150)
+	public void onSimpleEventFirst(SimpleEvent event) {
+		++hits;
+		assertEquals(1, hits);
+	}
+}

src/test/java/dev/kske/eventbus/SimpleEvent.java

@@ -0,0 +1,9 @@
+package dev.kske.eventbus;
+
+/**
+ * A simple event for testing purposes.
+ *
+ * @author Kai S. K. Engelbart
+ * @since 0.0.1
+ */
+public class SimpleEvent implements IEvent {}