#19912 added support for WebFilter. However, there is not a way to only test a WebFilter with it. This means anyone testing only WebFilter objects must mock a Controller, ApplicationContext, or RouterFunction to test the WebFitler.
It would be nice if there was a way that allowed testing just the WebFilter.
Testing a WebFilter is more low level than the other bindTo options. I was already considering a bindToHttpHandler variant as a natural addition to the other "mock server" bindTo variants that effectively result in using an HttpHandler.
This would cover any scenario that requires full control over the HttpHandler to test with including something like testing a single WebFilter: