API PULL - Validate MC connection in notifications

[puntope]

Changes proposed in this Pull Request:

Follow up for #2326 (comment)

This PR introduces a check for MC Connection in the NotificationService class before the notify() is sent.

Detailed test instructions:

0. Enable Notifications with the woocommerce_gla_notifications_enabled filter
1. With a connected MC - Go to the Connection test
2. Try the Notify function and see it worked
3. Disconnect MC
4. Try the Notify function
5. See it failed
6. Go to the logs and see the entry generated by the failure.

[puntope]

UNit test not running due a problem with the API for getting the plugin versions. Seems not related to this PR.

[codecov]

Codecov Report

Attention: Patch coverage is 70.00000% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 64.2%. Comparing base (8ceb779) to head (c9e9bc7).
Report is 53 commits behind head on feature/google-api-project.

Additional details and impacted files

@@                      Coverage Diff                       @@
##             feature/google-api-project   #2336     +/-   ##
==============================================================
+ Coverage                          64.1%   64.2%   +0.2%     
- Complexity                         4450    4478     +28     
==============================================================
  Files                               472     471      -1     
  Lines                             18775   18853     +78     
==============================================================
+ Hits                              12031   12110     +79     
+ Misses                             6744    6743      -1     

Flag	Coverage Δ
php-unit-tests	64.2% <70.0%> (+0.2%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
src/API/WP/NotificationsService.php	95.6% <100.0%> (+0.4%)	⬆️
src/Jobs/Notifications/AbstractNotificationJob.php	100.0% <ø> (ø)
src/Jobs/Notifications/CouponNotificationJob.php	100.0% <100.0%> (ø)
src/Jobs/Notifications/ProductNotificationJob.php	100.0% <100.0%> (ø)
...ernal/DependencyManagement/CoreServiceProvider.php	0.0% <0.0%> (ø)
src/ConnectionTest.php	0.0% <0.0%> (ø)

... and 5 files with indirect coverage changes

[jorgemd24]

Thanks @puntope for adding this! It works well 👍

Do you want to merge this to feature/google-api-project or add/grant-access-to-google-wpcom-app-in-setting-page, mainly because the other changes that you did are merged in grant-access-to-google-wpcom-app-in-setting-page

[puntope]

mainly because the other changes that you did are merged in grant-access-to-google-wpcom-app-in-setting-page

I did it in the main PR because I'm not using any function or service from the grant-access-to-google-wpcom-app-in-setting-page PR.

Do you think I should merge it in grant-access-to-google-wpcom-app-in-setting-page PR. instead?

[jorgemd24]

Hi @puntope, thanks for the clarification, actually I think it is better to merge it to feature/google-api-project so it is easier to review #2311