EasyMock - Creating mock of singleton created with enum

I'm generating the unit tests for my project, and I have a singleton class that looks like this

public enum MyEnum{
  INSTANCE;

  public String doSomething(String name){
      return "My name is "+name;
  }
}

This is how I was trying to do my unit test

@Test
public void test(){
    String name = "Nacho";
    String expectedResult = "My name is Nacho";
    String resultToSend = "My name is Nacho";
    MyEnum singletonMock = createNiceMock(MyEnum.class); //line A
    expect(singletonMock.doSomething(name)).andReturn(resultToSend);
    replay(singletonMock);
    String actualResponse = singleton.doSomething(mock);
    assertEquals(actualResponse, expectedResponse);
} 

I know this is a pointless test, but bare with me. My problem is that on line A, I get a runtime error saying "Cannot subclass final class class MyEnum", and I know that it's because enums are final.

Any ideas?