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.Statementpublic 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.BlockJUnit4ClassRunnerpublic class BlockJUnit4ClassRunner extends ParentRunner
    
     {    ...(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.ExpectExceptionpublic class ExpectException extends Statement{    private final Statement next;    private final Class
     expected;    public ExpectException(Statement next, Class
     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: