Where is my mocked user? How do I get him onto my context?

WhereIsMyMockedUser.cs

public GroupControllerTests()
{
    // do some other setup stuff first

    Mock<WebSecurity> webSecurity = new Mock<WebSecurity>(null, null);
    
    // only need a couple of properties, enough to build a string and stuff
    var currentUser = Mock.Of<IUser>(u =>
        u.IsApproved
        && u.Name == Utility.RandomString()
        && u.Id == Utility.RandomInt());
    
    // yup, user is set correctly
    webSecurity.Setup(x => x.CurrentUser).Returns(currentUser);

    // from GDev.Umbraco.Test - gives me umbracoContextMock and applicationContextMock
    var context = new ContextMocker();
    
    // in groupsController, umbracoContext.Security.CurrentUser is null.
    _groupsController = new GroupsController(context.UmbracoContextMock)
    {
        Request = new HttpRequestMessage(),
        Configuration = new HttpConfiguration()
    };
}