How can I mock an instance of an enum class with PowerMock & Mockito?

Question

I tried to follow the example offered in the answer to this very similar question, but it does not work for me. I get the following error message:

java.lang.IllegalArgumentException: Cannot subclass final class class com.myproject.test.support.ExampleEnumerable
    at org.mockito.cglib.proxy.Enhancer.generateClass(Enhancer.java:447)
    at org.mockito.cglib.core.DefaultGeneratorStrategy.generate(DefaultGeneratorStrategy.java:25)
    at org.mockito.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:217)
    at org.mockito.cglib.proxy.Enhancer.createHelper(Enhancer.java:378)
    at org.mockito.cglib.proxy.Enhancer.createClass(Enhancer.java:318)
    at org.powermock.api.mockito.repackaged.ClassImposterizer.createProxyClass(ClassImposterizer.java:123)
    at org.powermock.api.mockito.repackaged.ClassImposterizer.imposterise(ClassImposterizer.java:57)
    at org.powermock.api.mockito.internal.mockcreation.MockCreator.createMethodInvocationControl(MockCreator.java:110)
    at org.powermock.api.mockito.internal.mockcreation.MockCreator.mock(MockCreator.java:58)
    at org.powermock.api.mockito.PowerMockito.mock(PowerMockito.java:143)

I need a simple mock instance of an enum class. I don't need to mock any of its methods.

Here is the class I want to mock:

public enum ExampleEnumerable implements IEnumerable<ExampleEnumerable> {
    EXAMPLE_ENUM_1("Test Enum 1"),
    EXAMPLE_ENUM_2("Test Enum 2");

    final String alias;

    ExampleEnumerable(final String alias) {
        this.alias = alias;
    }

    @SuppressWarnings({"VariableArgumentMethod", "unchecked"})
    @Override
    public @Nullable
    String getAlias(final @Nonnull IEnumerable<? extends Enum<?>>... context) {
        return alias;
    }
}

I have the following TestNG setup:

import static org.powermock.api.mockito.PowerMockito.mock;

@PrepareForTest({ ExampleEnumerable.class})
@Test(groups = {"LoadableBuilderTestGroup"})
public class LoadableBuilderTest {

    private ExampleEnumerable mockEnumerable;

    @BeforeMethod
    public void setUp() {
        mockEnumerable = mock(ExampleEnumerable.class);
    }
}

Answer 1

You need to run this with PowerMockRunner

eg.

@RunWith(PowerMockRunner.class)
@PrepareForTest({ ExampleEnumerable.class})
@Test(groups = {"LoadableBuilderTestGroup"})
public class LoadableBuilderTest {
    private ExampleEnumerable mockEnumerable;

    @BeforeMethod
    public void setUp() {
        mockEnumerable = mock(ExampleEnumerable.class);
    }
}