How can I mock private static method with PowerMockito?

Question

I'm trying to mock private static method anotherMethod(). See code below

public class Util {     public static String method(){         return anotherMethod();     }      private static String anotherMethod() {         throw new RuntimeException(); // logic was replaced with exception.     } } 

Here is me test code

@PrepareForTest(Util.class) public class UtilTest extends PowerMockTestCase {          @Test         public void should_prevent_invoking_of_private_method_but_return_result_of_it() throws Exception {              PowerMockito.mockStatic(Util.class);             PowerMockito.when(Util.class, "anotherMethod").thenReturn("abc");              String retrieved = Util.method();              assertNotNull(retrieved);             assertEquals(retrieved, "abc");         }     } 

But every tile I run it I get this exception

java.lang.AssertionError: expected object to not be null 

I suppose that I'm doing something wrong with mocking stuff. Any ideas how can I fix it?

Answer 1

To to this, you can use PowerMockito.spy(...) and PowerMockito.doReturn(...).

Moreover, you have to specify the PowerMock runner at your test class, and prepare the class for testing, as follows:

@PrepareForTest(Util.class) @RunWith(PowerMockRunner.class) public class UtilTest {     @Test    public void testMethod() throws Exception {       PowerMockito.spy(Util.class);       PowerMockito.doReturn("abc").when(Util.class, "anotherMethod");        String retrieved = Util.method();        Assert.assertNotNull(retrieved);       Assert.assertEquals(retrieved, "abc");    } } 

Hope it helps you.

Answer 2

If anotherMethod() takes any argument as anotherMethod(parameter), the correct invocation of the method will be:

PowerMockito.doReturn("abc").when(Util.class, "anotherMethod", parameter);