Junit 验证exception的几种方法

1. try - catch

   @Test
   public void testInvalidData() {
       prepareTestData();
   
       try {
           userService.fetchUser(1234);
           Assert.fail("IllegalArgumentException not thrown");
       } catch (IllegalArgumentException expected) {
       }
   }

2. Annotation Attribute

   @Test(expected = IllegalArgumentException.class)
   public void testInvalidData() {
       prepareTestData();
   
       // should throw IllegalArgumentException
       userService.fetchUser(1234);
   }

   Junit5 以后不再有这个feature

3. Rule ExpectedException

   @Rule
   public ExpectedException thrown = ExpectedException.none();
   
   @Test
   public void testInvalidData() {
       prepareTestData();
   
       thrown.expect(IllegalArgumentException.class);
       userService.fetchUser(1234);
   }

   JUnit 4 contains the built-in rule ExpectedException. (please remember that JUnit 5 uses extensions instead of rules).

   This approach is similar to try-catch and @Test(expected = ...), but we can control from which point the exception is expected.

4. assertThrows

   @Test
   public void testInvalidData() {
       prepareTestData();
   
       Assertions.assertThrows(IllegalArgumentException.class, () -> {
           userService.fetchUser(1234);
       });
   }

   Assertions.assertThrows also returns the exception object to execute further asserts, e.g. to assert the message. 

 

Summary

I try to use assertThrows as often as possible because the test code gets both readable and flexible. But all the other mentioned approaches are also valid if correctly used.