Singleton and unit testing

Question

The Effective Java has the following statement on unit testing singletons

Making a class a singleton can make it difficult to test its clients, as it’s im

Answer 1

Use PowerMock to mock Singleton class (SingletonClassHelper) instance and non-static method (nonStaticMethod) which is called in task.execute().

    import static org.mockito.Mockito.when;

    import org.junit.Before;
    import org.junit.Test;
    import org.junit.runner.RunWith;
    import org.mockito.InjectMocks;
    import org.mockito.Mock;
    import org.mockito.Mockito;
    import org.powermock.api.mockito.PowerMockito;
    import org.powermock.core.classloader.annotations.PrepareForTest;
    import org.powermock.modules.junit4.PowerMockRunner;

    @PrepareForTest({ SingletonClassHelper.class })
    @RunWith(PowerMockRunner.class)
    public class ClassToTest {

        @InjectMocks
        Task task;

        private static final String TEST_PAYLOAD = "data";
        private SingletonClassHelper singletonClassHelper;


        @Before
        public void setUp() {
            PowerMockito.mockStatic(SingletonClassHelper.class);
            singletonClassHelper = Mockito.mock(SingletonClassHelper.class);
            when(SingletonClassHelper.getInstance()).thenReturn(singletonClassHelper);
        }

        @Test
        public void test() {
            when(singletonClassHelper.nonStaticMethod(parameterA, parameterB, ...)).thenReturn(TEST_PAYLOAD);
            task.execute();
        }
    }