前言
在上次的博客中我们提到了最终由Runner以Notifier为参数执行测试样例，但并没有解释到底测试方法是如何被运行起来的，一些诸如RunWith、RunAfter之类的特性又到底是如何实现的呢。这次我们就集中深入Runner的运行机制来探究样例是如何被运行的。
包装注解信息——FrameWorkMember
首先我们需要把注解等用户配置信息收集起来并attach到对应的方法、类和属性上，为了在之后的代码中能够方便的取到这些信息，我们要包装原有的类、方法和域，分别如下。
TestClass
TestClass包含原有的clazz信息，并且维护了两个Map来管理它所包含的方法与属性，每个map的键是注解，而值是标上注解的FrameWorkMethod或FrameWorkField。同时TestClass还默认内置两个Comparator来排序自己所包含的方法和属性。
下面给出如何构造一个TestClass的代码。
public TestClass(Class<?> clazz) {
this.clazz = clazz;
if (clazz != null && clazz.getConstructors().length > 1) {
throw new IllegalArgumentException(
"Test class can only have one constructor");
}
Map<Class<? extends Annotation>, List<FrameworkMethod>> methodsForAnnotations =
new LinkedHashMap<Class<? extends Annotation>, List<FrameworkMethod>>();
Map<Class<? extends Annotation>, List<FrameworkField>> fieldsForAnnotations =
new LinkedHashMap<Class<? extends Annotation>, List<FrameworkField>>();
scanAnnotatedMembers(methodsForAnnotations, fieldsForAnnotations);
this.methodsForAnnotations = makeDeeplyUnmodifiable(methodsForAnnotations);
this.fieldsForAnnotations = makeDeeplyUnmodifiable(fieldsForAnnotations);
}
protected void scanAnnotatedMembers(Map<Class<? extends Annotation>, List<FrameworkMethod>> methodsForAnnotations, Map<Class<? extends Annotation>, List<FrameworkField>> fieldsForAnnotations) {
for (Class<?> eachClass : getSuperClasses(clazz)) {
for (Method eachMethod : MethodSorter.getDeclaredMethods(eachClass)) {
addToAnnotationLists(new FrameworkMethod(eachMethod), methodsForAnnotations);
}
// ensuring fields are sorted to make sure that entries are inserted
// and read from fieldForAnnotations in a deterministic order
for (Field eachField : getSortedDeclaredFields(eachClass)) {
addToAnnotationLists(new FrameworkField(eachField), fieldsForAnnotations);
}
}
}TestClass的主要功能就是向Runner提供clazz信息以及附带的注解信息，上文的addToAnnotationLists将对应member加入该annotation映射的member列表。下面给一个TestClass的方法列表截图，大家可以感受一下。
FrameWorkMethod
我们先给出它的父类FrameWorkMember的定义
public abstract class FrameworkMember<T extends FrameworkMember<T>> implements
Annotatable {
abstract boolean isShadowedBy(T otherMember);
boolean isShadowedBy(List<T> members) {
for (T each : members) {
if (isShadowedBy(each)) {
return true;
}
}
return false;
}
protected abstract int getModifiers();
/**
* Returns true if this member is static, false if not.
*/
public boolean isStatic() {
return Modifier.isStatic(getModifiers());
}
/**
* Returns true if this member is public, false if not.
*/
public boolean isPublic() {
return Modifier.isPublic(getModifiers());
}
public abstract String getName();
public abstract Class<?> getType();
public abstract Class<?> getDeclaringClass();
}
FrameWorkMethod包装了方法信息以及方法相关的注解以及一些基本的验证方法比如validatePublicVoid和是否被其他FrameWorkMethod覆盖的判断方法，除父类要求外它主要提供的信息如下：
Annotations
Method
ReturnType
ParameterTypes
FrameWorkField
同FrameWorkMethod差不多，FrameWorkField和它继承自同一父类，较为简单，此处就不再详细介绍了。
真正的执行单元——Statement
Statement是最小的执行单元，诸如RunAfter、RunWith等功能均是通过嵌套Statement来实现的，下面我们先给出Statement的定义，再给出一个嵌套的例子。
public abstract class Statement {
/**
* Run the action, throwing a {@code Throwable} if anything goes wrong.
*/
public abstract void evaluate() throws Throwable;
}下面以RunAfter的实现为例来说明：
public class RunAfters extends Statement {
private final Statement next;
private final Object target;
private final List<FrameworkMethod> afters;
public RunAfters(Statement next, List<FrameworkMethod> afters, Object target) {
this.next = next;
this.afters = afters;
this.target = target;
}
@Override
public void evaluate() throws Throwable {
List<Throwable> errors = new ArrayList<Throwable>();
try {
next.evaluate();
} catch (Throwable e) {
errors.add(e);
} finally {
for (FrameworkMethod each : afters) {
try {
each.invokeExplosively(target);
} catch (Throwable e) {
errors.add(e);
}
}
}
MultipleFailureException.assertEmpty(errors);
}
}可以看出新的Statement执行时会先执行旧有的Statement，再将附加上的一系列方法以target为参数运行。
组合方法测试的Runner实现——BlockJunitClassRunner
Junit使用虚类ParentRunner来管理复合的Runner，使用composite模式，而BlockJunitClassRunner是ParentRunner的一个子类，主要负责同一测试类多个方法的组合测试，也就是最常用的情形。我们首先还是聚焦在如何运行测试样例上。
首先看ParentRunner如何实现run方法
@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);
}
}这里有个classBlock方法用来提供真正运行的Statement，下面我们看一看
protected Statement classBlock(final RunNotifier notifier) {
Statement statement = childrenInvoker(notifier);
if (!areAllChildrenIgnored()) {
statement = withBeforeClasses(statement);
statement = withAfterClasses(statement);
statement = withClassRules(statement);
}
return statement;
}这个过程就是先通过反射获得初始Statement，然后附加上RunBefore、RunAfter、用户自定义Rule，我们来看一下初始Statement是如何生成的。
其过程是先取得所有通过过滤器的Childeren，再使用内置的调度器来分别按顺序调用runChild方法，下面我们给出BlockJunit4ClassRunner的runChild方法
@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);
}
}这里面最重要的就是RunLeaf也就是原子测试方法以及如何为单个方法生成的Statement——methodBlock，我们在下面分别给出。
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();
}
}RunLeaf的逻辑并不难，先通知Notifier测试开始，再直接调用statement的evaluate方法，最后通知Notifier测试结束。我们再来看看statement是如何生成的。
protected Statement methodBlock(final FrameworkMethod method) {
Object test;
try {
test = new ReflectiveCallable() {
@Override
protected Object runReflectiveCall() throws Throwable {
return createTest(method);
}
}.run();
} catch (Throwable e) {
return new Fail(e);
}
Statement statement = methodInvoker(method, test);
statement = possiblyExpectingExceptions(method, test, statement);
statement = withPotentialTimeout(method, test, statement);
statement = withBefores(method, test, statement);
statement = withAfters(method, test, statement);
statement = withRules(method, test, statement);
return statement;
}
上述代码的逻辑还是比较复杂的，这里简单概述一下，首先构造测试类的实例，然后为对应method构造statement的子类InvokeMethod，然后调用FrameWorkMethod的反射运行方法，如下：
public class InvokeMethod extends Statement {
private final FrameworkMethod testMethod;
private final Object target;
public InvokeMethod(FrameworkMethod testMethod, Object target) {
this.testMethod = testMethod;
this.target = target;
}
@Override
public void evaluate() throws Throwable {
testMethod.invokeExplosively(target);
}
}组合类测试的Runner实现——Suite
Suite是对于ParentRunner的另一子类实现，主要用于多个测试类的情形。Suite自己维护一个runner列表，实现了getChilderen方法，其层次是在上文中提到的runChildren里，这一部分需要取出children节点然后调用runChild方法。我们着重考察suite和BlockJunit4ClassRunner在getChildren和runChild方法上的区别。Suite通过用户传入的runnerBuilder为每个类单独建立runner作为children返回，而后者则返回带Test注解的FrameWorkMethod列表。使用getChildren拿到的runner直接运行run方法。下面我们给出RunnerBuilder是如何为一系列测试类提供一系列对应的Runner，说来也简单，就是使用为单个类建立Runner的方法为每个测试类建立最后组成一个集合。但是此处需要防止递归——this builder will throw an exception if it is requested for another runner for {@code parent} before this call completes（说实话这段如何防止递归我也没看懂，有看懂的兄弟求教）。对于Suite而言，一般就是它维护一个BlockJUnit4ClassRunner列表。
public abstract class RunnerBuilder {
private final Set<Class<?>> parents = new HashSet<Class<?>>();
/**
* Override to calculate the correct runner for a test class at runtime.
*
* @param testClass class to be run
* @return a Runner
* @throws Throwable if a runner cannot be constructed
*/
public abstract Runner runnerForClass(Class<?> testClass) throws Throwable;
/**
* Always returns a runner, even if it is just one that prints an error instead of running tests.
*
* @param testClass class to be run
* @return a Runner
*/
public Runner safeRunnerForClass(Class<?> testClass) {
try {
return runnerForClass(testClass);
} catch (Throwable e) {
return new ErrorReportingRunner(testClass, e);
}
}
Class<?> addParent(Class<?> parent) throws InitializationError {
if (!parents.add(parent)) {
throw new InitializationError(String.format("class '%s' (possibly indirectly) contains itself as a SuiteClass", parent.getName()));
}
return parent;
}
void removeParent(Class<?> klass) {
parents.remove(klass);
}
/**
* Constructs and returns a list of Runners, one for each child class in
* {@code children}. Care is taken to avoid infinite recursion:
* this builder will throw an exception if it is requested for another
* runner for {@code parent} before this call completes.
*/
public List<Runner> runners(Class<?> parent, Class<?>[] children)
throws InitializationError {
addParent(parent);
try {
return runners(children);
} finally {
removeParent(parent);
}
}
public List<Runner> runners(Class<?> parent, List<Class<?>> children)
throws InitializationError {
return runners(parent, children.toArray(new Class<?>[0]));
}
private List<Runner> runners(Class<?>[] children) {
List<Runner> runners = new ArrayList<Runner>();
for (Class<?> each : children) {
Runner childRunner = safeRunnerForClass(each);
if (childRunner != null) {
runners.add(childRunner);
}
}
return runners;
}
}
在注解中加上参数
BlockJUnit4ClassRunnerWithParameters
Junit使用BlockJUnit4ClassRunnerWithParameters继承BlockJUnit4ClassRunner来完成对于组合方法的带参数测试。它覆写了createTest方法和对构造器和域的验证方法。
@Override
public Object createTest() throws Exception {
InjectionType injectionType = getInjectionType();
switch (injectionType) {
case CONSTRUCTOR:
return createTestUsingConstructorInjection();
case FIELD:
return createTestUsingFieldInjection();
default:
throw new IllegalStateException("The injection type "
+ injectionType + " is not supported.");
}
}Parameterized
Parameterized继承了Suite，用来完成对多个类的组合测试的带参数版本。它提供三大注解——Parameters、Parameter、UseParametersRunnerFactory，前两者是用来指定参数的，后者用来指定对于每一个测试类如何生成Runner的工厂,默认工厂返回BlockJUnit4ClassRunnerWithParameters。我们下面给出内置的工厂类如何创建runner的代码。
private List<Runner> createRunnersForParameters(
Iterable<Object> allParameters, String namePattern,
ParametersRunnerFactory runnerFactory) throws Exception {
try {
List<TestWithParameters> tests = createTestsForParameters(
allParameters, namePattern);
List<Runner> runners = new ArrayList<Runner>();
for (TestWithParameters test : tests) {
runners.add(runnerFactory
.createRunnerForTestWithParameters(test));
}
return runners;
} catch (ClassCastException e) {
throw parametersMethodReturnedWrongType();
}
}
private List<Runner> createRunners() throws Throwable {
Parameters parameters = getParametersMethod().getAnnotation(
Parameters.class);
return Collections.unmodifiableList(createRunnersForParameters(
allParameters(), parameters.name(),
getParametersRunnerFactory()));
}
java
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