在 Mockito Junit 测试中发生检查异常时要断言或期望什么

Question

How to run a JUnit Test case on Checked Exception. For eg HttpClient execute method shows checked IOException but i am not sure what to assert/expect.

HttpClient httpClient = mock(HttpClient.class)



 try {
            when(httpClient.execute(any(HttpPost.class))).thenThrow(IOException.class);
//Ideally nothing should work after this as exception is thrown
        //fail("This will fail") // this statement will throw Assertion Error
    }
    catch (IOException io) {
    
    }

If i try using expected method, this returns IOException never thrown.

 Exception thrown =
                  assertThrows(
                          IOException.class,
                          () -> {
                           when(httpClient.execute(any(HttpPost.class))).thenThrow(IOException.class);
                          });
    
          Truth.assertThat(thrown).hasMessageThat().contains("IOException");
        }

Answer 1

If I correctly understood, You need annotation @Test. And you should assign field "expected" your exception class.

@Test(excepted = IOException.class)
testMethod() {
     throw new IOException();
}

Answer 2

In your test method you only stubbed httpClient.execute method, but never called it. That is why no exception has been thrown.

On top of that:

• it is unclear what is object under test. Mock collaborators, not object under test.
• if you only assert on message containing "IOException" string, you may prefer to assert that it is the instance of that class.