public void ValidateAndRegisterUserIfNotExist_WithExistingUser_ShouldNotRegisterUser() { // Arrange . const string email = "*****@*****.**"; var name = new Tuple <string, string>("Ananth", "Tatachar"); var userName = $"{name.Item1} {name.Item2}"; _userInfoProvider.GetFirstAndLastNames(userName) .ReturnsForAnyArgs(name); _userInfoProvider.GetUser(name, email).ReturnsForAnyArgs(new User { UserId = 1, FirstName = name.Item1, LastName = name.Item2, Email = email }); // Act . _target.ValidateAndRegisterUserIfNotExist($"{name.Item1} {name.Item2}", email); // Assert . _userInfoProvider.DidNotReceive().RegisterUser(name, email); }