public class AccountController : Controller
{

    public IMembershipService MembershipService { get; set; }

    protected override void Initialize(RequestContext requestContext)
    {
        if (MembershipService == null) { MembershipService = new AccountMembershipService(); }

        base.Initialize(requestContext);
    }

    public AccountController(IMembershipService membership)
    {
        MembershipService = membership;
    }

  [HttpPost]
    public ActionResult Login(LoginModel model, string ReturnUrl)
    {
        if (ModelState.IsValid)
        {
            if (MembershipService.ValidateUser(model.EmailorUserName, model.Password))
            {
            .....
            }
        }
   }

public class AccountControllerTest2
{
    [Test]
    public void Login_UserCanLogin()
    {
        string returnUrl = "/Home/Index";
        string userName = "user1";
        string password = "password1";

        Mock<AccountMembershipService> Membership = new Mock<AccountMembershipService>();
        AccountController Controller = new AccountController(Membership.Object);

        var model = new LoginModel
        {
            EmailorUserName = userName,
            Password = password
        };

        var result = Controller.Login(model, returnUrl) as RedirectResult;

        Assert.NotNull(result);
        Assert.AreEqual(returnUrl, result.Url);
    }
}

<membership defaultProvider="CustomMembershipProvider">
  <providers>
    <clear />
    <add name="CustomMembershipProvider" type="QUBBasketballMVC.Infrastructure.CustomMembershipProvider" connectionStringName="UsersContext" enablePasswordRetrieval="false" enablePasswordReset="true" requiresQuestionAndAnswer="false" requiresUniqueEmail="false" maxInvalidPasswordAttempts="5" minRequiredPasswordLength="6" minRequiredNonalphanumericCharacters="0" passwordAttemptWindow="10" applicationName="/" />
  </providers>
</membership>

Mock<IMembershipService> Membership = new Mock<IMembershipService>();

if (MembershipService == null)
   MembershipService = new AccountMembershipService();