public void GetSharePriceDidntExistTest() { // Arrange var shareRepositoryMock = Substitute.For <ISharesRepository>(); var sut = new SharesService(shareRepositoryMock); int shareID = 135; shareRepositoryMock .DoesShareExists(Arg.Is <int>(shareID)) .Returns(false); // Act sut.GetSharePrice(shareID); // Asserts shareRepositoryMock.DidNotReceive().GetSharePrice(Arg.Is <int>(shareID)); }