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Testing NoSubscriberEvent Handling in greenrobot/EventBus

This test suite validates the handling of NoSubscriberEvent scenarios in the EventBus library, ensuring proper event handling when no subscribers are present or when subscription-related errors occur.

Test Coverage Overview

The test suite provides comprehensive coverage of NoSubscriberEvent handling scenarios in EventBus.

Tests basic NoSubscriberEvent generation when no subscribers exist
Verifies event behavior after subscriber unregistration
Tests error handling with problematic NoSubscriberEvent subscribers
Validates EventBus instance and original event preservation

Implementation Analysis

The testing approach employs JUnit framework features to systematically verify EventBus’s NoSubscriberEvent functionality.

Key patterns include:

Subscriber registration/unregistration lifecycle testing
Exception handling verification using BadNoSubscriberSubscriber
Event tracking through AbstractEventBusTest inheritance
Custom event subscription using @Subscribe annotations

Technical Details

Testing infrastructure includes:

JUnit 4 testing framework
EventBus builder configuration for logging control
Custom subscriber classes for edge case testing
AbstractEventBusTest base class for common functionality
@Subscribe annotation for event handling

Best Practices Demonstrated

The test suite exemplifies several testing best practices:

Isolated test cases for specific scenarios
Proper test method naming conveying purpose
Thorough exception handling verification
Clean setup and teardown through inheritance
Clear separation of test scenarios and subscriber implementations

greenrobot/eventbus

EventBusTestJava/src/main/java/org/greenrobot/eventbus/EventBusNoSubscriberEventTest.java

            
/*
 * Copyright (C) 2012-2016 Markus Junginger, greenrobot (http://greenrobot.org)
 *
 * 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
 *
 *      http://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 org.greenrobot.eventbus;

import org.junit.Test;

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertSame;

/**
 * @author Markus Junginger, greenrobot
 */
public class EventBusNoSubscriberEventTest extends AbstractEventBusTest {

    @Test
    public void testNoSubscriberEvent() {
        eventBus.register(this);
        eventBus.post("Foo");
        assertEventCount(1);
        assertEquals(NoSubscriberEvent.class, lastEvent.getClass());
        NoSubscriberEvent noSub = (NoSubscriberEvent) lastEvent;
        assertEquals("Foo", noSub.originalEvent);
        assertSame(eventBus, noSub.eventBus);
    }

    @Test
    public void testNoSubscriberEventAfterUnregister() {
        Object subscriber = new DummySubscriber();
        eventBus.register(subscriber);
        eventBus.unregister(subscriber);
        testNoSubscriberEvent();
    }

    @Test
    public void testBadNoSubscriberSubscriber() {
        eventBus = EventBus.builder().logNoSubscriberMessages(false).build();
        eventBus.register(this);
        eventBus.register(new BadNoSubscriberSubscriber());
        eventBus.post("Foo");
        assertEventCount(2);

        assertEquals(SubscriberExceptionEvent.class, lastEvent.getClass());
        NoSubscriberEvent noSub = (NoSubscriberEvent) ((SubscriberExceptionEvent) lastEvent).causingEvent;
        assertEquals("Foo", noSub.originalEvent);
    }

    @Subscribe
    public void onEvent(NoSubscriberEvent event) {
        trackEvent(event);
    }

    @Subscribe
    public void onEvent(SubscriberExceptionEvent event) {
        trackEvent(event);
    }

    public static class DummySubscriber {
        @SuppressWarnings("unused")
        @Subscribe
        public void onEvent(String dummy) {
        }
    }

    public class BadNoSubscriberSubscriber {
        @Subscribe
        public void onEvent(NoSubscriberEvent event) {
            throw new RuntimeException("I'm bad");
        }
    }

}