How do you test HttpContext with a CascadingParameter in Blazor?

[rob-king-volpara]

I've read through the documentation and from what I can work out, I shbould be able to do this:

DefaultHttpContext httpContext = new();
httpContext.Request.Form = new FormCollection([]);
httpContext.Session = new Mock<ISession>().Object;

IRenderedComponent<Applications> cut = testContext.RenderComponent<Applications>(p => p
    .Add(p => p.HttpContext, httpContext)
);

return Verify(cut);

Where the component I'm testing just has:

@code {
    [CascadingParameter]
    public HttpContext HttpContext { get; set; }

But when I try to run the tests, I always get this error:

Test method Components.Pages.ApplicationsTests.Applications_UnauthorizedUser_RendersMessage threw exception: 
System.InvalidOperationException: Collection was modified; enumeration operation may not execute.

If I debug the test, it seems to be running the component fine and I get all the way to the Verify(...) call. If I inspect the cut, it is showing the correct markup. The test just fails while Verify is doing its compare, I think.

Any ideas?

[rob-king-volpara]

It's always the way..... right after posting this it started working when I changed the test methods from Task to void.

Might be useful to my future self or someone else if they hit this.