这有效：

@RunWith(PowerMockRunner.class)
@PrepareForTest(ABC.class)
public class ABCTest {

    @Test
    public void finalCouldBeMock() {
        final ABC abc = PowerMockito.mock(ABC.class);
        PowerMockito.when(abc.myMethod()).thenReturn("toto");
        assertEquals("toto", abc.myMethod());
    }
}