You could use a pattern like DI (Dependency Injection). In your case, I would pass a RoleProvider to the AccountController, which would be the default RoleProvider by default, and a mock object in your tests. Something like:

public class AccountController
{
    private MembershipProvider _provider;
    private RoleProvider roleProvider;

    public AccountController()
      : this(null, null)
    {
    }

    public AccountController(MembershipProvider provider, RoleProvider roleProvider)
    {
      _provider = provider ?? Membership.Provider;
      this.roleProvider = roleProvider ?? System.Web.Security.Roles.Provider;
    }
}

The MVC runtime will call the default constructor, which in turn will initialize the AccountController with the default role provider. In your unit test, you can directly call the overloaded constructor, and pass a MockRoleProvider (or use Moq to create it for you):

[Test]
public void AccountControllerTest()
{
    AccountController controller = new AccountController(new MockMembershipProvider(), new MockRoleProvider());
}

EDIT: And here s how I mocked the entire HttpContext, including the principal user. To get a Moq version of the HttpContext:

public static HttpContextBase GetHttpContext(IPrincipal principal)
{
  var httpContext = new Mock<HttpContextBase>();
  var request = new Mock<HttpRequestBase>();
  var response = new Mock<HttpResponseBase>();
  var session = new Mock<HttpSessionStateBase>();
  var server = new Mock<HttpServerUtilityBase>();
  var user = principal;


  httpContext.Setup(ctx => ctx.Request).Returns(request.Object);
  httpContext.Setup(ctx => ctx.Response).Returns(response.Object);
  httpContext.Setup(ctx => ctx.Session).Returns(session.Object);
  httpContext.Setup(ctx => ctx.Server).Returns(server.Object);
  httpContext.Setup(ctx => ctx.User).Returns(user);

  return httpContext.Object;
}

A mock implementation of Principal:

  public class MockPrincipal : IPrincipal
  {
    private IIdentity _identity;
    private readonly string[] _roles;

    public MockPrincipal(IIdentity identity, string[] roles)
    {
      _identity = identity;
      _roles = roles;
    }

    public IIdentity Identity
    {
      get { return _identity; }
      set { this._identity = value; }
    }

    public bool IsInRole(string role)
    {
      if (_roles == null)
        return false;
      return _roles.Contains(role);
    }
  }

A MockIdentity:

public class MockIdentity : IIdentity
  {
    private readonly string _name;

    public MockIdentity(string userName)    {
      _name = userName;
    }

    public override string AuthenticationType
    {
      get { throw new System.NotImplementedException(); }
    }

    public override bool IsAuthenticated
    {
      get { return !String.IsNullOrEmpty(_name); }
    }

    public override string Name
    {
      get { return _name; }
    }
  }

And the magic call:

MockIdentity identity = new MockIdentity("JohnDoe");
var httpContext = MoqHelpers.GetHttpContext(new MockPrincipal(identity, null));

Note that I edited the code above to leave out some custom stuff, but I m quite sure this should still work.

Now I run into another problem when I try to test the ChangePassword() method in ASP.NET MVC.

        try
        {
            if (MembershipService.ChangePassword(User.Identity.Name, currentPassword, newPassword))
            {
                if (!TempData.ContainsKey("ChangePassword_success"))
                {
                    TempData.Add("ChangePassword_success", true);
                }

                return PartialView("ChangePassword");

            }

Now I get that User is null, when I reach this line. In my testclass I have:

mockMembershipService.Setup(cp => cp.ChangePassword("johndoe", currentPassword, newPassword)).Returns(true);

I thought that this would work, but it doesn t care for that I send "johndoe". And If I were to mock IPrincipal, the User property is readonly.

TypeMock Isolator does mocking of statics etc. But I second (and +1 d) Razzie s answer.

I have done what you coded, but I still get that User is null when it reaches:

mockMembershipService.Setup(cp => cp.ChangePassword("johndoe", currentPassword, newPassword)).Returns(true);

In my Testclass I have:

        //Arrange (Set up a scenario)
        var mockMembershipService = new Mock<IMembershipService>();
        MockIdentity identity = new MockIdentity("JohnDoe");
        var httpContext = MoqHelpers.GetHttpContext(new MockPrincipal(identity, null));
        var controller = new AccountController(null, mockMembershipService.Object, null, null, null);
        string currentPassword = "qwerty";
        string newPassword = "123456";
        string confirmPassword = "123456";

        // Expectations

         mockMembershipService.Setup(pw => pw.MinPasswordLength).Returns(6);
         mockMembershipService.Setup(cp => cp.ChangePassword("johndoe", currentPassword, newPassword)).Returns(true);

Do I call my cp.ChangePassword with wrong parameters? And should MVCContrib Testhelpers classes be able to mock Http context and so on? I just can t find info for how to setup User.Identity.Name with MVCContrib. I have used this from a tutorial to test something (mock) session:

        var builder = new TestControllerBuilder();
        var controller = new AccountController(mockFormsAuthentication.Object, mockMembershipService.Object, mockUserRepository.Object, null, mockBandRepository.Object);
        builder.InitializeController(controller);

EDIT: I have come a little further:

        MockIdentity identity = new MockIdentity("JohnDoe");
        var httpContext = MoqHelpers.GetHttpContext(new MockPrincipal(identity, null));
        var controller = new AccountController(null, mockMembershipService.Object, null, null, null);
        controller.ControllerContext = new ControllerContext(httpContext, new RouteData(), controller);

but my now I can t get my cp.ChangePassword in the expectation to return true:

mockMembershipService.Setup(cp => cp.ChangePassword("johndoe", currentPassword, newPassword)).Returns(true);

I am sending "johndoe" string, because, it requires a string as a parameter for User.Identity.Name, but it doesn t return true.