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JUnit 注解@Rule的工作原理 junitSAPSAP云平台JavaSAP Cloud Platform 

程序员文章站 2022-04-16 12:43:13
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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.

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

 

JUnit 注解@Rule的工作原理
            
    
    
        junitSAPSAP云平台JavaSAP Cloud Platform 

 

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.

 

JUnit 注解@Rule的工作原理
            
    
    
        junitSAPSAP云平台JavaSAP Cloud Platform 

 

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:

 

JUnit 注解@Rule的工作原理
            
    
    
        junitSAPSAP云平台JavaSAP Cloud Platform 

 

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

 

JUnit 注解@Rule的工作原理
            
    
    
        junitSAPSAP云平台JavaSAP Cloud Platform 

 

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.

 

JUnit 注解@Rule的工作原理
            
    
    
        junitSAPSAP云平台JavaSAP Cloud Platform 

 

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<IllegalArgumentException>()
        {

            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:

 

JUnit 注解@Rule的工作原理
            
    
    
        junitSAPSAP云平台JavaSAP Cloud Platform JUnit 注解@Rule的工作原理
            
    
    
        junitSAPSAP云平台JavaSAP Cloud Platform 

 

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JUnit 注解@Rule的工作原理
            
    
    
        junitSAPSAP云平台JavaSAP Cloud Platform