The API to trigger semantics actions from tests right now is not very discoverable:

Instead of requiring developers to figure that out, we should provide an easier way. Similarly to WidgetTester.tap [1] and WidgetTester.tapAt [2] we should provide a simple API on WidgetTester itself to trigger semantics actions in tests based on finders. With such an API, people could be writing something like the following in their tests:

  await tester.performSemanticsAction(find.text('click me'), SemanticsAction.tap);

[1] https://master-api.flutter.dev/flutter/flutter_test/WidgetController/tap.html
[2] https://master-api.flutter.dev/flutter/flutter_test/WidgetController/tapAt.html