前言
尽管在第二次博客中我们讲述了Runner的运行机制,但是许多其他特性比如Filter是如何与运行流程结合却并不清楚。这次我们来回顾整理一下Junit的执行流程,给出各种特性生效的机理,并分析一些代码中精妙的地方。
Junit的执行流程
JUnitCore的RunMain方法,使用jUnitCommandLineParseResult解析参数并生成Request。
Result runMain(JUnitSystem system, String... args) {
system.out().println("JUnit version " + Version.id());
JUnitCommandLineParseResult jUnitCommandLineParseResult = JUnitCommandLineParseResult.parse(args);
RunListener listener = new TextListener(system);
addListener(listener);
return run(jUnitCommandLineParseResult.createRequest(defaultComputer()));
}
在jUnitCommandLineParseResult的createRequest方法中,调用Request的classes方法生成Request,并对生成的Request进行过滤
public Request createRequest(Computer computer) {
if (parserErrors.isEmpty()) {
Request request = Request.classes(
computer, classes.toArray(new Class<?>[classes.size()]));
return applyFilterSpecs(request);
} else {
return errorReport(new InitializationError(parserErrors));
}
}
接下来我们就要进入核心部分了,先提出以下几个问题:
如何为单个类生成Request
Filter的实现机制
对于错误如何把它纳入以Request为初始并最终使用Runner的run这一套机制中
我们先回答第一个问题,其他问题我们会在之后慢慢解答:
接下来先给出classes方法的代码
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) {
return runner(new ErrorReportingRunner(e, classes));
}
}
问题再次被拆分为三个:
生成一个Builder
从Builder导出一个Runner
从Runner生成一个Request
AllDefaultPossibilitiesBuilder的逻辑是先后使用ignoredBuilder、annotatedBuilder、suiteMethodBuilder、junit3Builder、junit4Builder来生成Runner直到有一个成功则返回,然后getSuite方法将返回的Runner变为Suite。
Computer的作用是包装从builder生成Runner的逻辑,提供两种方案——生成SingleClassRunner和Suite。我们在这里提一下生成Suite的逻辑,就是使用该builder不停为多个测试类生成对应的Runner并放置到Suite的Runner列表中,Suite其他的初始化过程依从其父类,此处就不详述。
最后从Runner生成Request也异常简单,也就是实现其getRunner方法返回该Runner。现在我们把注意力投放到builder如何导出Runner,以JUnit4Builder为例,下面给出代码:
public class JUnit4Builder extends RunnerBuilder {
@Override
public Runner runnerForClass(Class<?> testClass) throws Throwable {
return new BlockJUnit4ClassRunner(testClass);
}
}
可以看出它其实就是直接生成了一个BlockJUnit4ClassRunner,下面我们关注该Runner的构造过程。
protected ParentRunner(Class<?> testClass) throws InitializationError {
this.testClass = createTestClass(testClass);
validate();
}
protected TestClass createTestClass(Class<?> testClass) {
return new TestClass(testClass);
}
可以看出构造SingleClassRunne的过程就是解析生成TestClass的过程,我们在第二篇博客里已经详细讲解过了,此处就不再赘述了。可能许多读者看到这儿会很困惑,之前一直强调的描述测试样例的Description到底是在哪里生成的呢?其实是在Runner的run过程里生成的,如下:
@Override
public void run(final RunNotifier notifier) {
EachTestNotifier testNotifier = new EachTestNotifier(notifier,
getDescription());
try {
Statement statement = classBlock(notifier);
statement.evaluate();
} catch (AssumptionViolatedException e) {
testNotifier.addFailedAssumption(e);
} catch (StoppedByUserException e) {
throw e;
} catch (Throwable e) {
testNotifier.addFailure(e);
}
}
@Override
public Description getDescription() {
Description description = Description.createSuiteDescription(getName(),
getRunnerAnnotations());
for (T child : getFilteredChildren()) {
description.addChild(describeChild(child));
}
return description;
}
可以明显地得知Description是依据Runner来建立的,它的结构和Runner应该保持一致,它是Runner的附属品,用来供与Runner交互的Notifier获得信息。
Junit的Failure机制
下面我们主要关注在运行之后Result的生成和Failure的处理。Result是Notifier通过fireTestRunFinished(result)生成的,我们来看一看它具体做了什么。
private abstract class SafeNotifier {
private final List<RunListener> currentListeners;
SafeNotifier() {
this(listeners);
}
SafeNotifier(List<RunListener> currentListeners) {
this.currentListeners = currentListeners;
}
void run() {
int capacity = currentListeners.size();
List<RunListener> safeListeners = new ArrayList<RunListener>(capacity);
List<Failure> failures = new ArrayList<Failure>(capacity);
for (RunListener listener : currentListeners) {
try {
notifyListener(listener);
safeListeners.add(listener);
} catch (Exception e) {
failures.add(new Failure(Description.TEST_MECHANISM, e));
}
}
fireTestFailures(safeListeners, failures);
}
abstract protected void notifyListener(RunListener each) throws Exception;
}
public void fireTestRunFinished(final Result result) {
new SafeNotifier() {
@Override
protected void notifyListener(RunListener each) throws Exception {
each.testRunFinished(result);
}
}.run();
}
public void fireTestAssumptionFailed(final Failure failure) {
new SafeNotifier() {
@Override
protected void notifyListener(RunListener each) throws Exception {
each.testAssumptionFailure(failure);
}
}.run();
}
private void fireTestFailures(List<RunListener> listeners,
final List<Failure> failures) {
if (!failures.isEmpty()) {
new SafeNotifier(listeners) {
@Override
protected void notifyListener(RunListener listener) throws Exception {
for (Failure each : failures) {
listener.testFailure(each);
}
}
}.run();
}
}
简单概括一下,就是调用它所管理的Listener的testRunFinished来处理Result,处理完毕之后就把该Listener标记为安全的,如果处理过程中出现异常,则将该异常加入failures列表,全部通知完毕后再次通知所有安全的Listener处理之前所有的Failure。这里还有一个问题,那就是Failure到底是怎样在运行时生成的。由于断言机制,所有的断言失败都会抛出对应的异常,对于断言异常,请看下文:
@Override
protected void runChild(final FrameworkMethod method, RunNotifier notifier) {
Description description = describeChild(method);
if (isIgnored(method)) {
notifier.fireTestIgnored(description);
} else {
Statement statement;
try {
statement = methodBlock(method);
}
catch (Throwable ex) {
statement = new Fail(ex);
}
runLeaf(statement, description, notifier);
}
}
Fail会直接抛出原有的异常,再次调用RunLeaf
protected final void runLeaf(Statement statement, Description description,
RunNotifier notifier) {
EachTestNotifier eachNotifier = new EachTestNotifier(notifier, description);
eachNotifier.fireTestStarted();
try {
statement.evaluate();
} catch (AssumptionViolatedException e) {
eachNotifier.addFailedAssumption(e);
} catch (Throwable e) {
eachNotifier.addFailure(e);
} finally {
eachNotifier.fireTestFinished();
}
}
最后转入addFailure处理,而addFailure会最终通知Notifier中的各个Listener处理
。那JunitCore到底使用了怎样的Listener,它又执行了怎样的操作。
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;
}
注意JunitCore的Run方法中加入了一个Result中内置的Listener,其定义如下
@RunListener.ThreadSafe
private class Listener extends RunListener {
@Override
public void testRunStarted(Description description) throws Exception {
startTime.set(System.currentTimeMillis());
}
@Override
public void testRunFinished(Result result) throws Exception {
long endTime = System.currentTimeMillis();
runTime.addAndGet(endTime - startTime.get());
}
@Override
public void testFinished(Description description) throws Exception {
count.getAndIncrement();
}
@Override
public void testFailure(Failure failure) throws Exception {
failures.add(failure);
}
@Override
public void testIgnored(Description description) throws Exception {
ignoreCount.getAndIncrement();
}
@Override
public void testAssumptionFailure(Failure failure) {
// do nothing: same as passing (for 4.5; may change in 4.6)
}
}
可以看出该Listener在testFailure中完成了添加Failure的动作,看到这里我简直激动莫名,使用一个内置的Listener子类来避免显式为Result添加Failure,而是依然把这些操作集中在Notifier——Listener的观察者体系里,可谓精妙绝伦!
同时还需注意在runMain方法中加入了一个TextListener来完成打印结果的工作。
Junit的初始化错误处理
上面我们讲述了Junit如何处理样例中的断言错误以及运行时错误,但是当初始化Request的过程中一旦发生异常依然需要继续运行并提示测试失败,这又是怎么实现的呢?
我们回顾之前createRequest方法中的errorReport,代码如下:
public static Request errorReport(Class<?> klass, Throwable cause) {
return runner(new ErrorReportingRunner(klass, cause));
}
我们来看一下这个ErrorReportingRunner的实现
public class ErrorReportingRunner extends Runner {
private final List<Throwable> causes;
private final String classNames;
public ErrorReportingRunner(Class<?> testClass, Throwable cause) {
this(cause, new Class<?>[] { testClass });
}
public ErrorReportingRunner(Throwable cause, Class<?>... testClasses) {
if (testClasses == null || testClasses.length == 0) {
throw new NullPointerException("Test classes cannot be null or empty");
}
for (Class<?> testClass : testClasses) {
if (testClass == null) {
throw new NullPointerException("Test class cannot be null");
}
}
classNames = getClassNames(testClasses);
causes = getCauses(cause);
}
@Override
public Description getDescription() {
Description description = Description.createSuiteDescription(classNames);
for (Throwable each : causes) {
description.addChild(describeCause(each));
}
return description;
}
@Override
public void run(RunNotifier notifier) {
for (Throwable each : causes) {
runCause(each, notifier);
}
}
private String getClassNames(Class<?>... testClasses) {
final StringBuilder builder = new StringBuilder();
for (Class<?> testClass : testClasses) {
if (builder.length() != 0) {
builder.append(", ");
}
builder.append(testClass.getName());
}
return builder.toString();
}
@SuppressWarnings("deprecation")
private List<Throwable> getCauses(Throwable cause) {
if (cause instanceof InvocationTargetException) {
return getCauses(cause.getCause());
}
if (cause instanceof InitializationError) {
return ((InitializationError) cause).getCauses();
}
if (cause instanceof org.junit.internal.runners.InitializationError) {
return ((org.junit.internal.runners.InitializationError) cause)
.getCauses();
}
return Arrays.asList(cause);
}
private Description describeCause(Throwable child) {
return Description.createTestDescription(classNames, "initializationError");
}
private void runCause(Throwable child, RunNotifier notifier) {
Description description = describeCause(child);
notifier.fireTestStarted(description);
notifier.fireTestFailure(new Failure(description, child));
notifier.fireTestFinished(description);
}
}
上面的大致逻辑依然是先生成Description(因为没有到ParentRunner的run那一步,Description没有生成,故需要在此生成),然后移交给Notifier处理
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