public void WhenAddingSeedToScoreHouse() { //ARRANGE IScoreHouse mock = Substitute.For <IScoreHouse>(); int counter = 1; mock.When(x => x.AddSeed(new Seed())) .Do(x => counter++); //ACT mock.AddSeed(new Seed()); mock.AddSeed(new Seed()); //ASSERT Assert.AreEqual(1, counter); }