Note: For simplicity, this tutorial does not follow the “Test Driven
Development” approach. If you’re more comfortable with that style of
development, you can always go that route.

4. Write a test for our class

Inside the counter_test.dart file, write the first unit test. Tests are
defined using the top-level test function, and you can check if the results
are correct by using the top-level expect function.
Both of these functions come from the test package.

5. Combine multiple tests in a group

If you have several tests that are related to one another,
combine them using the group function provided by the test package.

6. Run the tests

Now that you have a Counter class with tests in place,
you can run the tests.

Run tests using IntelliJ or VSCode