How to mock a method in an ENUM class?

Question

I am working on writing JUNIT test case for my below ENUm class. My below class will only give me the hostname for the current machine where I am running my code. While I am writing JUNIT test, how can I mock the below class, so that I can change getHostName() method whenever I want to so that whenever I am calling getDatacenter(), it can return me whatever hostname I am passing by mocking it. I don't want to make it as a parametrized.

I just want to test certain cases while changing the hostname while mocking it.

public enum DatacenterEnum {
    DEV, DC1, DC2, DC3;


    public static String forCode(int code) {
    return (code >= 0 && code < values().length) ? values()[code].name() : null;
    }
    private static final String getHostName() {
        try {
            return InetAddress.getLocalHost().getCanonicalHostName().toLowerCase();
        } catch (UnknownHostException e) {
            s_logger.logError("error = ", e);
        }

        return null;
    }

    public static String getDatacenter() {
        return getHostName();
    }
}

Answer 1

It is possible, but this is not recommended, it would be better to refactor the code.

Working example with Mockito/PowerMock

@RunWith(PowerMockRunner.class)
@PrepareForTest(DatacenterEnum.class)
public class DatacenterEnumTest {

    @Mock
    InetAddress inetAddress;

    @Test
    public void shouldReturnDatacenter() throws UnknownHostException {
        //given
        mockStatic(InetAddress.class);
        given(inetAddress.getCanonicalHostName()).willReturn("foo");
        given(InetAddress.getLocalHost()).willReturn(inetAddress);

        //when
        String datacenter = DatacenterEnum.getDatacenter();

        //then
        assertThat(datacenter).isEqualTo("foo");
    }
}

Dependencies

• org.powermock:powermock-module-junit4:1.5.2
• org.powermock:powermock-api-mockito:1.5.2
• org.assertj:assertj-core:1.5.0
• junit:junit:4.11