public void Login_Login_Failed()
{
// arrange
var loggedInUser = new UserModel();
loggedInUser.AddError("invalid username or password");
this._contactService.Setup(x => x.Login(It.IsAny <string>(), It.IsAny <string>())).Returns(Task.FromResult <UserModel>(loggedInUser));
ILoginViewModel loginViewModel = this.CreateSubject();
// act
loginViewModel.ShowDialog();
loginViewModel.UserName = "******";
loginViewModel.Password = "******";
loginViewModel.LoginCommand.Execute(null);
// assert
Assert.IsNull(loginViewModel.DialogResult);
this._contactService.Verify(x => x.Login(It.IsAny <string>(), It.IsAny <string>()), Times.Once);
}