How can a Blazored Modal be unit tested? (I'm using the bUnit framework.)

My modal component has a CascadingParameter BlazoredModalInstance. Clicking "OK" calls BlazoredModalInstance.CloseAsync(), and cancelling calls BlazoredModalInstance.CancelAsync(). The Blazored Modal works fine in my application. (Thanks for the good work!)

Since BlazoredModalInstance is a class, I can't use a mock to check if CloseAsync or CancelAsync have been called.

I can construct a BlazoredModalInstance object in the test and supply it as a parameter to a surrounding my modal component under test, but when e.g. CloseAsync is called, I get a NullReferenceException at Blazored.Modal.BlazoredModalInstance.d__72.MoveNext().

Do I need set up the initial state of this test BlazoredModalInstance object more, e.g., by calling some other methods on it?

I had hoped for something more like IModalService. I am able to unit test the code to show my modal (e.g., IModalService.Show). It's very easy to mock IModalService and IModalReference in order to test my modal from the "outside". But I can't figure out how to test the modal from the "inside".

Originally posted by @linestandard in #311