FakeNavigationManager can't be used in non-render scenarios

[robertmclaws]

Describe the Bug

My company ships a product called Breakdance, which is a unit testing framework that (among other things) integrates with Microsoft IHost model to let you do cleaner unit testing that involves Dependency Injection.

We also ship a product called BlazorEssentials, which (among other things) provides a robust MVVM framework for Blazor WebAssembly.

We recently updated our Breakdance.Blazor library to be a FailoverServiceProvider for our BUnitTestContext. In doing so, we discovered the FakeNavigationManager is a more fully-featured service than our TestableNavigationManager, so we removed our version.

The problem now is that we can't test our ViewModels anymore without moving all of our code to execute inside a BUnitTestContext, because your NavigationManager requires a renderer to function.

Expected Behavior:

I would expect to be able to inject a NavigationManager in non-render scenarios.

Requested Fix:

We would like you to please create a new, blank constructor that does not throw an ArgumentNullException on the lack of renderer, and adjust the code so that it doesn't fail if a renderer is not present.

Version info:

• bUnit version: Latest
• .NET Runtime and Blazor version: 6.x
• OS type and version: Windows 11

[egil]

Hi @robertmclaws,

Admittedly we never considered users would use our FakeNavigationManager without a TestContext. If I understand your request correctly, you want all the functionality, but only perform the raise the NotifyLocationChanged event inside the renderers dispatcher if one is available. Otherwise just do it without?

[linkdotnet]

Hey @robertmclaws maybe a bit of background to understand why this renderer.Dispatcher.InvokeAsync is needed in the first place. Just imagine you have a component which does something on the LocationChanged event. And imagine some user changes UI content like a label or what not. Now in your production code you don't have any problem, because there is only one thread. But the whole situation changes when we are in a test: Without the Dispatcher.InvokeAsync the function which is attached to theLocationChanged-event would get triggered from the test-thread and not the blazor thread, which will lead to an exception. Well that is very inconvenient for the user. The user could do something like that:

// The button would trigger a LocationChanged event
cut.InvokeAsync(() => cut.Find("button").Click());

But that is very noisy and technical. So to "catch" that problem, we just route your events through the dispatcher on our own.

[linkdotnet]

I would close this bug as "works as intended". It is the way we are using the NavigationManager, which is not intended to be used without a TestContext (mainly because it is a helper for your Blazor components). Almost every functionality is under the TestContext umbrella in some way or another.

That said using a lot of the bUnit objects outside the TestContext or Blazor environment will not work at all. So yes, we could not invoke the Dispatcher if it is null, but I am not sure if this is a common-enough use cases.