public void Add_CategoryToDbSetCategories_When_Valid() { // Arrange var fakeDrumsAcademyContext = new Mock <IDrumsAcademyContext>(); var fakeCategoriesDbSet = QueryableDbSetMock.GetQueryableMockDbSetFromList(this.GetCategories()); fakeDrumsAcademyContext.Setup(f => f.Categories).Returns(fakeCategoriesDbSet); var sut = new Services.Data.CategoryService(fakeDrumsAcademyContext.Object); var category = new Category() { Id = Guid.NewGuid(), Type = CategoryType.Theory }; var categoriesCount = fakeCategoriesDbSet.Count(); // Act sut.AddCategory(category); categoriesCount += 1; // Assert Assert.AreEqual(categoriesCount, fakeCategoriesDbSet.Count()); }