Use case

We want to test platform views (including webviews) in our flutter integrations tests. Flutter integration tests currently don't support this. To workaround this, we'd like to use adb to interact with the app. For adb to be able to interact with the app during the test, we need to set pointerEventSource to TestBindingEventSource.test.

Unfortunately, flutter_test doesn't seem to support setting pointerEventSource yet... I think we can create a setter for it, or make withPointerEventSource. Thanks!