JUnit4.12 源码分析之Statement

1. Statement

• 抽象类Statement作为命令模式的Command,只有一个方法
• 各种Runner作为命令模式中的Invoker,将发出各种Statement,来表示它们运行JUnit测试的整个过程;
• org.junit.internal.runners.statement包中定义了Statement的子类(具体命令),来处理针对方法
  的标注,如@Test,@Before,@After,@BeforeClass,@AfterClass;

// org.junit.runners.model.Statement
public abstract class Statement{

    public abstract void evalute() throws Throwable;

}

// BlockJUnit4ClassRunner 中的符合命令,来处理 @Test, @Before, @After...
// org.junit.runners.BlockJUnit4ClassRunner

public class BlockJUnit4ClassRunner extends ParentRunner<FrameworkMethoc>{
    ...(略)

    protected Statement methodBlock(FrameworkMethod method){
        Object test;
        try{
            test = new ReflectiveCallable(){
                @Override
                protected Object runReflectiveCall() throws Throwable{
                    return createTest();
                }
            }.run();
        }catch(Throwable e){
            return new Fail(e);
        }

        // 各种Statement
        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;
    }

    // 根据反射,执行无参构造函数
    protected Object createTest() throws Exception{
        return getTestClass().getOnlyConstructor().newInstance();
    }

    // Statement builders
    protected Statement methodInvoker(FrameworkMethod method, Object test){
        return new InvokeMethod(method, test);
    }
}

2.Statement 的实现类

• org.junit.internal.runners.statements包下
  • ExpectException
  • Fail
  • FailOnTimeOut
  • InvokeMethod
  • RunAfters
  • RunBefores

// @Test(expected=IndexOutOfBoundsException.class)

// 源码 org.junit.internal.runners.statements.ExpectException
public class ExpectException extends Statement{
    private final Statement next;
    private final Class<? extends Throwable> expected;

    public ExpectException(Statement next, Class<? extends Throwable> expected){
        this.next = next;
        this.expected = expected;
    }

    @Override
    public void evalute() throws Exception{
        boolean complete = false;
        try{
            next.evalute();
            complete = true;
        }catch(AssumptionViolatedException e){
            throw e;
        }catch(Throwable e){
            if(!expected.isAssignableFrom(e.getClass())){
                String message = "Unexpected exception, expected<"
                        + expected.getName() + "> but was<"
                        + e.getClass().getName() + ">";
                throw new Exception(messge, e);
            }
        }
        if(complete){
            throw new AssertionError("Expected exception: "
                    + expected.getName());
        }
    }
}

参考资料:

• JUnit4.8.2 Statement之复合命令
• JUnit4.10 Statement