Mocking the Membership Provider

[Fact]
public void HowToMockMembershipProvider()
{
  // create fake membership user
  var user = new Sitecore.FakeDb.Security.Accounts.FakeMembershipUser();

  // create membership provider mock
  var provider =
    NSubstitute.Substitute.For<System.Web.Security.MembershipProvider>();
  provider.GetUser(@"extranet\John", true).Returns(user);

  // switch the membership provider
  using (new Sitecore.FakeDb.Security.Web.MembershipSwitcher(provider))
  {
    // check if the user exists
    var exists = Sitecore.Security.Accounts.User.Exists(@"extranet\John");
    Xunit.Assert.True(exists);
  }
}