Unit test for void method

Question

I need to write unit test for some static void methods with an unknown/unpredictable side effect. For example

public void doSth() {
    try {
        HttpPostUtil.sendRequest("abc", "xyz");
    } catch(Exception ex) {
        ex.printStackTrace();
    }
}

HttpPostUtil is in another jar file. It is out of my control and it will post the data to some web services . What is the testing methodology that we could do in this situation? ( PowerMockito is not allowed here :()

Answer 1

Because it is void method the only thing you can test is behaviour. In such situation you have few options

1. Wrap calls to HttpPostUtil with an object in order to not have it as a static and mock it in tests (by mockito or by injection of your implementation into your object). This is called sprout class.
2. Wrap call to HttpPostUtil into the method and override it in test suite to something else.

Generally speaking - if it is hard to test -> it is hard to use -> implementation is bad -> so it needs refactoring, not tuning the tests.

Answer 2

While testing a method, you should always just test that method and mock the other calls to other methods. Because the other methods should have been tested in their own test methods.

Here you simply need 2 tests if you also want to test the catch case. With Mockito:

@InjectMocks
private YourClass yourClass;

@Mock
private HttpPostUtil httpPostUtil;

@Test
public void testDoSthPositive() {
    // Run Test
    yourClass.doSth();

    // Control
    verify(httpPostUtil).sendRequest("abc", "xyz");
    verifyNoMoreInteractions(httpPostUtil);  // Optional
}

@Test
public void testDoSthNegative() {
    // Preparation
    NullPointerException exceptionMock = mock(NullPointerException.class);
    doThrow(exceptionMock).when(httpPostUtil).sendRequest("abc", "xyz");

    // Run Test
    yourClass.doSth();

    // Control
    verify(exceptionMock).printStackTrace();
    verifyNoMoreInteractions(exceptionMock, httpPostUtil);  // Optional
}