public void SetUp() { _file = new [] { "Console.WriteLine()" }; _existingLicense = new Mock <ILicense>(); _existingLicense.Setup(x => x.RemoveFrom(_file)).Returns(_file); _newLicense = new Mock <ILicense>(); _newLicense.Setup(x => x.AddTo(_file)).Returns(_file); var subject = new ChangedSource(_file, _existingLicense.Object, null); _result = subject.Add(_newLicense.Object); }