Add direct event bus contract tests

src/test/java/com/livingworld/events/EventBusTest.java

@@ -0,0 +1,54 @@
+package com.livingworld.events;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertSame;
+
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
+import org.junit.jupiter.api.Test;
+
+class EventBusTest {
+
+    @Test
+    void listenerReceivesPublishedEventExactlyOnce() {
+        LivingWorldEventBus bus = new LivingWorldEventBus();
+        AtomicInteger calls = new AtomicInteger();
+        AtomicReference<LivingWorldEvent> received = new AtomicReference<>();
+        BaseLivingWorldEvent event = event("test_event");
+        bus.register(event.eventType(), published -> {
+            calls.incrementAndGet();
+            received.set(published);
+        });
+
+        bus.publish(event);
+
+        assertEquals(1, calls.get());
+        assertSame(event, received.get());
+    }
+
+    @Test
+    void multipleListenersReceiveTheSameEvent() {
+        LivingWorldEventBus bus = new LivingWorldEventBus();
+        AtomicInteger calls = new AtomicInteger();
+        bus.register("test_event", event -> calls.incrementAndGet());
+        bus.register("test_event", event -> calls.incrementAndGet());
+        bus.register("test_event", event -> calls.incrementAndGet());
+
+        bus.publish(event("test_event"));
+
+        assertEquals(3, calls.get());
+    }
+
+    @Test
+    void unknownEventTypeDoesNotCrash() {
+        LivingWorldEventBus bus = new LivingWorldEventBus();
+
+        assertDoesNotThrow(() -> bus.publish(event("unknown")));
+        assertEquals(1, bus.getPublishedEventCount());
+    }
+
+    private static BaseLivingWorldEvent event(String type) {
+        return new BaseLivingWorldEvent(type, 1L, "test");
+    }
+}