Fixed mutable state test

gistfile1.java

@Test
public void changeNameTest() {
  MutableClass original_name = new MutableClass("my name");
  MutableClass expected_name = new MutableClass("my name");

  NameFilter filter = new NameFilter();
  MutableClass new_name = filter.changeName(original_name,
                                            "new name");

  assertEquals(new_name, expected_name);
}