Create a unit test for the count state class.
Details
The app should build off of the app from a previous activity that used state to count button presses by adding the following:
a file that runs tests of the CountModel class.
a group of tests.
a test for:
the constructor.
the increment function called once.
the increment function called twice.
Example
$ flutter test test/count_model_test.dart
00:20 +3: All tests passed!