Create widget tests for the count app.
Details
The app should build off of the app from a previous activities that used state to count button presses by adding the following:
a file that runs widget tests for the count text.
a widget test for:
the count initially being 0.
the count being 1 after a single tap
the count being 2 after two taps.
Example
$ flutter test test/count_widget_test.dart
00:07 +3: All tests passed!