Mocking singleton with PowerMockito

Question

in order to test one of the private method I coded, I need to mock a Singleton.

After testing several methods with PowerMockito :

PowerMockito.mockStatic(UtilDatabaseSoldeAutoCdeCommon.class);
Mockito.when(UtilDatabaseSoldeAutoCdeCommon.getInstance()).thenReturn(mockDatabase);

I could never mock this class. Thus I cannot test my methods as in every of them, I access to database.

UtilDatabaseSoldeAutoCdeCommon is defined as such :

public class UtilDatabaseSoldeAutoCdeCommon extends AbstractUtilDatabase {

private static UtilDatabaseSoldeAutoCdeCommon instance;

private UtilDatabaseSoldeAutoCdeCommon() {
    super();
}

public static UtilDatabaseSoldeAutoCdeCommon getInstance() {
    if(instance == null) {
        instance = new UtilDatabaseSoldeAutoCdeCommon();
    }
    return instance;
}

...
}

I debugged powermockito when it calls getInstance() but everytime consructor is called, it crashes as it tries to load configuration file (which does not exist).

I precise that config file is defined as a constant in absract parent class of UtilDatabaseEnrichissement and used in constructor.

How could I test this part ?

Answer 1

I think this should work:

    @PrepareForTest({UtilDatabaseSoldeAutoCdeCommon.class})
    public class SomeTest {
        @Mock
        UtilDatabaseSoldeAutoCdeCommon fakeSingletonInstance;   

        @Test
        public void test() {
             Whitebox.setInternalState(UtilDatabaseSoldeAutoCdeCommon.class, "instance", fakeSingletonInstance);
             // Write here your test
        }
    }

Answer 2

This question was asked long time back and I was facing similar issue and unable to find good answers hence answering it now. I tested the class with suppressing constructor like

PowerMockito.suppress(UtilDatabaseSoldeAutoCdeCommon.class.getConstructors());