Could you please help me in writing unit test cases for this component? #668

Sure. What is your exact problem here? Do you want to check that the roles of your viewmodel are in the select element?
Basically you have to do a few things

1. Create a view model which you then inject into your Component. You can see here how this is done
2. To get the select you can use var selectElement = cut.Find("select").Unwrap() as IHtmlSelectElement Of course if you have multiple select elements you should use an Id or a class. But with that you have access to all selectElement.Options which should reflect all your roles from the ViewModel.

So very simplified something like that:

[Fact]
public void Test()
{
   this.AddTestAuthorization().SetAuthorized("username"); // Needed for the AuthorizeAttribute
   // Setup our test data aka ViewModel
   var viewModel = new ViewModel
   {
       Roles = new string[] { ... },
       User = new User { ... },
   };
   Services.AddScoped(_ => viewModel); // Put our ViewModel in the DI container
   var cut = RenderComponent<MyComponent>();

   var select = cut.Find("select").Unwrap() as IHtmlSelectElement;

   select.Options.Length.Should().Be(3); // Depends how many roles you have setup in the ViewModel
   select.Options[0].Value.Should().Be("Admin"); // Depends how you setup the ViewModel
}

I can't really help you further for many reasons: For staterts yiz did not share the ViewModel nor the base class you are deriving from.
So I would suggest try to implement the test and if you have a specific issue we can look together.

As you also have async stuff in your code, you might want to have a look at this.