Suppose you need to repeatedly execute some test method in your unit test case, for example, you would like to test getPrice based on the first set of test data 5 times in test method test1() while for the second set of test data, only one time should be executed.

创新互联公司专注为客户提供全方位的互联网综合服务，包含不限于网站设计制作、网站设计、平川网络推广、小程序开发、平川网络营销、平川企业策划、平川品牌公关、搜索引擎seo、人物专访、企业宣传片、企业代运营等，从售前售中售后，我们都将竭诚为您服务，您的肯定，是我们最大的嘉奖；创新互联公司为所有大学生创业者提供平川建站搭建服务，24小时服务热线：18980820575，官方网址：www.cdcxhl.com

The below class RepeatDemoOne is a bad example, where this special LOOP operation is mixed with test method implementation.

Ideally the test method should only contain the pure logic to operate on the method being tested. So we have a better solution RepeatDemoTwo: It could easily be observed that now the test method test1 and test2 are rather clean: no more for LOOP and System.out.println exist any more.

Instead, I put the LOOP logic and print out operation into class RepeatableRule which implements interface MethodRule. The concrete rule implementation is done by overriding method apply as below:

class RepeatableRule implements MethodRule{  
    int times = 1;  
    String[] testMethods = null;  
    RepeatableRule(int times, String[] testMethods){  
        this.times = times;  
        this.testMethods = testMethods;  
    }  
    @Override  
    public Statement apply(final Statement base, final FrameworkMethod method, Object target) {  
      return new Statement() {  
         @Override  
         public void evaluate() throws Throwable {  
            int loopTime = 1;  
            if(Arrays.asList(testMethods).contains(method.getName())) {  
                loopTime = times;  
            }    
            for(int i = 0; i < loopTime; i++ ) { 
                base.evaluate(); 
                System.out.println(method.getName() + " executed.");
            }
         }  
      };  
    }  }

When I execute this test case, I can get exactly the same result as RepeatDemoOne:

With the help of @Rule, we can achieve the same as @Test(expected=).

For example, we can use an instance of class ExpectedException to manually declare within a test method itself that a test method expects a given type of exception class.

Besides exception, we can also manually specify a sub string which is expected to appear in an error message, and add our custom error message in Junit report if a test method fails. See following code for example:

public class RuleWithException {
    @Rule
    public ExpectedException exp = ExpectedException.none();
    @Test
    public void expectMessage()
    {
        exp.expectMessage("Hello World");
        throw new RuntimeException("Hello World will throw exception.");
    }
    @Test
    public void expectCourse()
    {
        exp.expectCause(new BaseMatcher()
        {
            public boolean matches(Object item)
            {
                return item instanceof IllegalArgumentException;
            }
            @Override
            public void describeTo(org.hamcrest.Description description) {
                description.appendText("Expected exception with type IllegalArgumentException "
                        + "raised in test method! ");
            }
        });
        Throwable cause = new IllegalArgumentException("Cause Test.");
        throw new RuntimeException(cause);
    }}

In this example, if we comment out line 46, the customed message defined in method describeTo will be printed out in JUnit console:

要获取更多Jerry的原创文章，请关注公众号"汪子熙":