public void Check_That_Right_Method_Was_Called_Inside_IsUserNameAvailable_Action() { // Arrange var mockUserService = new Mock <IUserService>(); mockUserService.Setup(m => m.UserExists(It.IsAny <string>())) .Returns(false); ValidationController validationController = GetValidationController(mockUserService: mockUserService); const string userName = "******"; // Act validationController.IsUserNameAvailable(userName); // Assert mockUserService.Verify(m => m.UserExists(userName)); }