This recipe demonstrates the core features provided by the test package
using the following steps:

Add the test or flutter_test dependency.

Create a test file.

Create a class to test.

Write a test for our class.

Combine multiple tests in a group.

Run the tests.

For more information about the test package,
see the test package documentation.

1. Add the test dependency

The test package provides the core functionality for 
writing tests in Dart. This is the best approach when
writing packages consumed by web, server, and Flutter apps.

dev_dependencies

test

<latest_version>

2. Create a test file

In this example, create two files: counter.dart and counter_test.dart.