How to android unit test and mock a static method

Question

Hi I really hope you can help me, I feel like I\'ve been pulling my hair out for days.

I\'m trying to write unit tests for a method A. Method A calls a static method

Answer 1

Static methods aren't related to any object - your helper.fetchUsernameFromInternet(...) is the same (but a bit confusing) as HelperUtils.fetchUsernameFromInternet(...) - you should even get a compiler warning due to this helper.fetchUsernameFromInternet.

What's more, instead of Mockito.mock to mock static methods you have to use: @RunWith(...), @PrepareForTest(...) and then PowerMockito.mockStatic(...) - complete example is here: PowerMockito mock single static method and return object

In other words - mocking static methods (and also constructors) is a bit tricky. Better solution is:

• if you can change HelperUtils, make that method non-static and now you can mock HelperUtils with the usual Mockito.mock

• if you can't change HelperUtils, create a wrapper class which delegates to the original HelperUtils, but doesn't have static methods, and then also use usual Mockito.mock (this idea is sometimes called "don't mock types you don't own")

Answer 2

You can use mockito latest version i.e 3.4.+ which allows static mocking

https://javadoc.io/doc/org.mockito/mockito-core/latest/org/mockito/Mockito.html#48

Answer 3

I did this way using PowerMockito.

I am using AppUtils.class, it contains multiple static methods and functions.

Static function:

public static boolean isValidEmail(CharSequence target) {
    return target != null && EMAIL_PATTERN.matcher(target).matches();
}

Test case:

@RunWith(PowerMockRunner.class)
@PrepareForTest({AppUtils.class})
public class AppUtilsTest {

    @Before
    public void setUp() throws Exception {
        MockitoAnnotations.initMocks(this);
        PowerMockito.mockStatic(AppUtils.class);

        PowerMockito.when(AppUtils.isValidEmail(anyString())).thenCallRealMethod();
    }

    @Test
    public void testValidEmail() {
        assertTrue(AppUtils.isValidEmail("name@email.com"));
    }

    @Test
    public void testInvalidEmail1() {
        assertFalse(AppUtils.isValidEmail("name@email..com"));
    }

    @Test
    public void testInvalidEmail2() {
        assertFalse(AppUtils.isValidEmail("@email.com"));
    }
}

Edit 1:

Add following imports:

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertNotNull;
import static org.junit.Assert.assertTrue;

Hope this would help you.

Answer 4

Here are some solutions:

• Modify your static method as a non-static method or wrap your static method with a non-static method, and then directly use Mockito to mock the non-static method in the Android Test.
• If you don't want to change any original code, you can try to use a dexmaker-mockito-inline-extended to mock static methods and final methods in the Android Test. I successfully mocked the static methods with it. Check this solution.
• Use a Robolectric in the Unit test and then use PowerMock to mock the static methods in the Unit Test.