I made the following test for my class: var mock = new Mock<IRandomNumberGenerator>(); mock.Setup(framework => framework.Generate(0, 50)) .Returns(7.0) var rnac = new RandomNumberAverageCounter(mock.Object, 1, 100); rnac.Run(); double result = rnac.GetAverage(); Assert.AreEqual(result, 7.0, 0.1); The problem here was that I changed my mind about what range of values Generate(int min, int max) would use. I ran the test and it failed. I know that that is what it's supposed to happen but I was left wondering if isn't there a way to launch an exception or throw in a message when trying to run the method params. Also, if I want to run this Generate() method 10 times with different values (let's say, from 1 to 10), will I have to make 10 mock setups or something, or is there a special method for it? The best I could think of is this (which isn't bad, I'm just asking if there is other better way): for (int i = 1; i < 10; ++i) { mock.Setup(framework => framework.Generate(1, 100)) .Returns((double)i); } Thanks