MD-WIDGETS: Create a pre-release testing script

Description

The pre-release testing script test/widget_test.dart is currently an auto-generated sample test file of the Flutter project. Modify it or create a new one before releasing the new version and make it a pre-release testing script for this package.

Why

1. Catch Bugs Early

   • It helps detect regressions or UI bugs before they reach users.
   • Especially important as the app grows in complexity.

2. Automate Repetitive Checks

   • We don’t have to manually test the same flows (e.g., button clicks, text input) every time — the script handles that.

3. Ensure Stable Releases

   • Before publishing a new version, running the test script can ensure no critical widget behaviour breaks.

4. Document Intended Behaviour

   • Test scripts also serve as living documentation of how widgets are expected to behave.

5. Save Time in the Long Run

   • Initial setup takes a bit of effort, but it saves a lot of debugging time later.