junit4.12源码分析-启动到选择runner

　　第一次写源代码分析，介绍运行流程和其中重要的类和接口！

　　JUnitCore

　　JUnitCore采用门面模式，可以启动junit4，junit3测试，也可以测试指定class。JUnitCore声明RunNotifier类，该类采用观察者模式实现事件管理。RunListener为测试事件基类，有测试开始结束失败等事件，如果想自定义事件可以继承该类。默认增加了两个RunListener，一个是TextListener，另一个是Result类函数createListener构造的Listener用于记录开始结束时间、执行总数、失败总数等。可看到run方法调用前触发了fireTestRunStarted，执行后触发了fireTestRunFinished。关键代码（截取）

    private final RunNotifier notifier = new RunNotifier();

    Result runMain(JUnitSystem system, String... args) {
        RunListener listener = new TextListener(system);
        addListener(listener);

        return run(jUnitCommandLineParseResult.createRequest(defaultComputer()));
    }

    public Result run(Request request) {
        return run(request.getRunner());
    }

    public Result run(Runner runner) {
        Result result = new Result();
        RunListener listener = result.createListener();
        notifier.addFirstListener(listener);
        try {
            notifier.fireTestRunStarted(runner.getDescription());
            runner.run(notifier);
            notifier.fireTestRunFinished(result);
        } finally {
            removeListener(listener);
        }
        return result;
    }

　　Request

　　对class和test的封装，可以是一个class下所有test、所有class下所有test、还可以结合filter。classes方法获取suite，suite里包含各个类的runner。关键代码（截取）

    public static Request classes(Computer computer, Class<?>... classes) {
        try {
            AllDefaultPossibilitiesBuilder builder = new AllDefaultPossibilitiesBuilder(true);
            Runner suite = computer.getSuite(builder, classes);
            return runner(suite);
        } catch (InitializationError e) {
            throw new RuntimeException(
                    "Bug in saff‘s brain: Suite constructor, called as above, should always complete");
        }
    }

　　RunnerBuilder

　　创建runner采用builder模式，对于每一个class产生一个runner。

    private List<Runner> runners(Class<?>[] children) {
        ArrayList<Runner> runners = new ArrayList<Runner>();
        for (Class<?> each : children) {
            Runner childRunner = safeRunnerForClass(each);
            if (childRunner != null) {
                runners.add(childRunner);
            }
        }
        return runners;
    }

　　AllDefaultPossibilitiesBuilder

　　选择具体builder，默认为junit4Builder,如果class有@Ignore标注则为IgnoredBuilder，如果class有@RunWith标注则为IgnoredBuilder，如果测试方法有suite则为SuiteMethodBuilder，如果class继承于junit.framework.TestCase则为JUnit38ClassRunner，否则默认时用JUnit4Builder返回BlockJUnit4ClassRunner

    public Runner runnerForClass(Class<?> testClass) throws Throwable {
        List<RunnerBuilder> builders = Arrays.asList(
                ignoredBuilder(),
                annotatedBuilder(),
                suiteMethodBuilder(),
                junit3Builder(),
                junit4Builder());

        for (RunnerBuilder each : builders) {
            Runner runner = each.safeRunnerForClass(testClass);
            if (runner != null) {
                return runner;
            }
        }
        return null;
    }