Hi Ben,
Isolator supports faking call chains so you should be able to do this:
Isolator.WhenCalled(() => ((Page)HttpContext.Current.CurrentHandler).ClientScript.RegisterClientScriptBlock(typeof(string),key, script)).IgnoreCall();
However, a way simpler way of doing this can be done by recursively faking - a recursive fake is a fake that returns a recursive fake for any method called on it. This means the entire call chain will be faked. In your case, you want the static methods of HttpContext to return recursive fakes:
Isolate.Fake.StaticMethods<HttpContext>(Members.ReturnRecursiveFakes);
And the entire chain following HttpContext will be faked.
Let me know if this helps.
Thanks,
Doron
Typemock Support