PowerMockito mock interface时报错org.powermock.reflect.exceptions.MethodNotFoundException

用例子说明：

有如下接口：

public interface MyTest {

    int plus(int a, String... s);
}

这样mock这个接口就会报错：org.powermock.reflect.exceptions.MethodNotFoundException: No method found with name 'plus' with parameter types: [ java.lang.Integer ]

@Before
public void setUp2() throws Exception {
    MyTest myTest = PowerMockito.mock(MyTest.class);
    PowerMockito.spy(myTest);
    PowerMockito.when(myTest, "plus", 1).thenReturn(2);
}

这样mock这个接口就对了：

@Before
public void setUp() throws Exception {
    MyTest myTest = PowerMockito.mock(MyTest.class);
    PowerMockito.spy(myTest);
    PowerMockito.when(myTest, "plus", 1, "a").thenReturn(2);
}