PowerMock: mocking of static methods (+ return original values in some particular methods)

Question

I use PowerMock 1.4.7 and JUnit 4.8.2

I need to mock only some static methods and I want others (from the same class) just to return original value. When I mock with mockStatic and don't call when().doReturn() all static methods return their defaults - like null when returning Object or false when returning boolean...etc. So I try to use thenCallRealMethod explicitly on each static method to return default implementation (means no mocking/ no fakes) but I don't know how to call it on every possible arguments variations (= I want for every possible input call original method). I only know how to mock concrete argument variation.

Answer 1

You can use a spy on your static class and mock only specific methods:

@RunWith(PowerMockRunner.class)
@PrepareForTest(MyStaticTest.MyStaticClass.class)
public class MyStaticTest {

public static class MyStaticClass {
    public static String getA(String a) {
        return a;
    }
    public static String getB(String b) {
        return b;
    }
}

@Test
public void should_partial_mock_static_class() throws Exception {
    //given
    PowerMockito.spy(MyStaticClass.class);
    given(MyStaticClass.getB(Mockito.anyString())).willReturn("B");
    //then
    assertEquals("A", MyStaticClass.getA("A"));
    assertEquals("B", MyStaticClass.getA("B"));
    assertEquals("C", MyStaticClass.getA("C"));
    assertEquals("B", MyStaticClass.getB("A"));
    assertEquals("B", MyStaticClass.getB("B"));
    assertEquals("B", MyStaticClass.getB("C"));
}

}

Answer 2

You can also use the stubbing API:

stub(method(MyStaticClass.class, "getB")).toReturn("B");

Edit:

To use stub and method statically import methods from these packages:

1. org.powermock.api.support.membermodification.MemberModifier
2. org.powermock.api.support.membermodification.MemberMatcher

For more info refer to the documentation

Answer 3

I managed to use spy and doReturn to achieve it.

class MyStatic {
    static String foo() { return "foo"; }
    static String foobar() { return foo() + "bar"; }
}

@Test
public void thisShouldSpyStaticMethods() {
    // arrange
    spy(MyStatic.class);
    doReturn("mocked foo").when(MyStatic.class);
    MyStatic.foo();

    // act
    final String result = MyStatic.foobar();

    // assert
    assertThat(result).isEqualTo("mocked foobar");
}

The doReturn followed by a call to the method to be mocked looks weird (at least to me), but seems to do the trick.

Using spy with when(MyStatic.foo()).thenReturn("mocked foo") doesn't work for me.

PowerMockito's documentation on mocking static method .

Answer 4

Based on this question PowerMockito mock single static method and return object

PowerMockito.mockStatic(MyStaticClass.class);

alone does not mock all methods (in recent versions of PowerMockito at least), only enables mocking later of individual methods.