I don't have a fix per se, but the root cause: This line AddSyncfusionBlazor does the following:

services.Replace(ServiceDescriptor.Singleton<IComponentActivator, SfComponentActivator>());

That interferes with how the ComponentFactories work:

// This is taken from the Bunit TestContextBase
Services.AddSingleton<IComponentActivator>(new BunitComponentActivator(ComponentFactories));

So essentially "our" activator gets replaced with SyncFusions one.

I am not sure why SyncFusion overrides the activator. But maybe something where we (@egil) have to add an extension point for 3rd party libraries so they can safely add their behavior without breaking the internals of bunit.

Ahh, yeah, remember thinking about this scenario of multiple IComponentActivator's competing.

We could change our implementation such that the BunitComponentActivator is instantiated in the TestRenderer and any other IComponentActivator registered in the service collection as input. It would then fall back to using that or to the default Blazor ComponnetActivator. That may be a good idea regardless, since the Blazor team may update theirs.

Fixed. There should be a release out in a few minutes.