Launcher概述

Launcher是JUnit5的启动类，也是对启动进行扩展的主要入口，扩展通过实现自定义的TestEngine来自定义测试类的发现和执行逻辑以达到定制化测试的目的

Launcher启动示例代码

public static void main(String[] args) {
        //设置搜索和过滤规则
        LauncherDiscoveryRequest request = LauncherDiscoveryRequestBuilder.request()
                .selectors(
                        selectPackage("zj"),
                        selectClass(*MyTest.class)
                )
                .filters(
                        includeClassNamePatterns(".*Tests")
                )
                .build();

        Launcher launcher = LauncherFactory.create();
        // Register a listener of your choice
        //通过监听器来监听获取执行结果
        TestExecutionListener listener = new SummaryGeneratingListener();
        launcher.registerTestExecutionListeners(listener);
        launcher.execute(request);
    }

启动分为如下几步：

1. 构造LauncherDiscoveryRequest指定测试类的查找和过滤规则

2. 通过 LauncherFactory.create()　来获取Launcher默认实现

3. 通过添加TestExecutionListener来进行测试结果的监听

4. 执行launcher.execute(req)方法启动测试

启动过程中涉及的类

DiscoverySelector

负责定义哪些资源可以被TestEngine用来寻找测试类，比如指定java类名或者指定目录路径

Filter

LauncherDiscoveryRequest

TestEngine

作为发现和执行符合LauncherDiscoveryRequest规则的测试的主要组件，对不同的编程模型可以实现自己的TestEngine，比如JupiterTestEngine

TestEngine在创建Launcher的时候通过JAVA SPI发现具体实现，JUnit5中有两种实现 ：JupiterTestEngine 和 VintageTestEngine

TestExecutionListener

定义了测试执行期间发生的事件类型，注册到Launcher的实现类将会在事件发生时得到通知

DefaultLauncher

做为Launcher的默认实现，持有TestEngine和TestExecutionListener集合，它们通过JAVA SPI发现，负责执行TestEngine来启动测试

各步骤详解

1. 构造LauncherDiscoveryRequest指定测试类的查找和过滤规则

	public LauncherDiscoveryRequest build() {
		LauncherConfigurationParameters launcherConfigurationParameters = new LauncherConfigurationParameters(
			this.configurationParameters);
		return new DefaultDiscoveryRequest(this.selectors, this.engineFilters, this.discoveryFilters,
			this.postDiscoveryFilters, launcherConfigurationParameters);
	}

2.利用LauncherFactory创建DefaultLauncher

	public static Launcher create() throws PreconditionViolationException {
		Launcher launcher = new DefaultLauncher(new ServiceLoaderTestEngineRegistry().loadTestEngines());
		for (TestExecutionListener listener : new ServiceLoaderTestExecutionListenerRegistry().loadListeners()) {
			launcher.registerTestExecutionListeners(listener);
		}
		return launcher;
	}

3. 通过添加TestExecutionListener来进行测试结果的监听

        TestExecutionListener listener = new SummaryGeneratingListener();
        launcher.registerTestExecutionListeners(listener);

4. 执行launcher.execute(req)方法启动测试

public void execute(LauncherDiscoveryRequest discoveryRequest, TestExecutionListener... listeners) {
		Preconditions.notNull(discoveryRequest, "LauncherDiscoveryRequest must not be null");
		Preconditions.notNull(listeners, "TestExecutionListener array must not be null");
		Preconditions.containsNoNullElements(listeners, "individual listeners must not be null");
		execute(discoverRoot(discoveryRequest, "execution"), discoveryRequest.getConfigurationParameters(), listeners);
	}

	private Root discoverRoot(LauncherDiscoveryRequest discoveryRequest, String phase) {
		Root root = new Root();

		for (TestEngine testEngine : this.testEngines) {
			// @formatter:off
			boolean engineIsExcluded = discoveryRequest.getEngineFilters().stream()
					.map(engineFilter -> engineFilter.apply(testEngine))
					.anyMatch(FilterResult::excluded);
			// @formatter:on

			if (engineIsExcluded) {
				logger.debug(() -> String.format(
					"Test discovery for engine '%s' was skipped due to an EngineFilter in phase '%s'.",
					testEngine.getId(), phase));
				continue;
			}

			logger.debug(() -> String.format("Discovering tests during Launcher %s phase in engine '%s'.", phase,
				testEngine.getId()));

			Optional<TestDescriptor> engineRoot = discoverEngineRoot(testEngine, discoveryRequest);
			engineRoot.ifPresent(rootDescriptor -> root.add(testEngine, rootDescriptor));
		}
		root.applyPostDiscoveryFilters(discoveryRequest);
		root.prune();
		return root;
	}

	private void execute(Root root, ConfigurationParameters configurationParameters,
			TestExecutionListener... listeners) {

		TestExecutionListenerRegistry listenerRegistry = buildListenerRegistryForExecution(listeners);
		TestPlan testPlan = TestPlan.from(root.getEngineDescriptors());
		TestExecutionListener testExecutionListener = listenerRegistry.getCompositeTestExecutionListener();
		testExecutionListener.testPlanExecutionStarted(testPlan);
		ExecutionListenerAdapter engineExecutionListener = new ExecutionListenerAdapter(testPlan,
			testExecutionListener);
		for (TestEngine testEngine : root.getTestEngines()) {
			TestDescriptor testDescriptor = root.getTestDescriptorFor(testEngine);
			execute(testEngine, new ExecutionRequest(testDescriptor, engineExecutionListener, configurationParameters));
		}
		testExecutionListener.testPlanExecutionFinished(testPlan);
	}

最后

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