Figure out why test results differ from search_api_opensearch

Hi, nice work for the recent updates of this module!

I think that elasticsearch_connector should be able to validate all tests from BackendTestBase.

My changes:
- call the parent testBackend
- fix the code so that all of these tests pass

Todo:
- Fix the unit tests with the changes I made
- Add PHPUnit\Asynchronicity back

Some notes on my changes:
- Some issues on the results were due to the fuzziness, I think a new issue for testing this features could be interesting
- The tests from searchSuccess where duplicate form the parent, I remove them

I would love your feedback.

I've removed the need for PHPUnit\Asynchronicity.
And updated the unit tests.

Adding 🌱 Plan for 8.0.0-alpha release Active as a parent issue.

Thanks @hexaki! I have looked the MR few times, on the first glance it looked like the changes where totally out-of-scope, but after more reading they make totally sense, excellent work! Its good that we're be able to also cover the parent testBackend! We should include that as release highlights for 8.0.0.

Only minor nitpick about the quotes,

Drupal does not have a hard standard for the use of single quotes vs. double quotes. Where possible, keep consistency within each module, and respect the personal style of other developers.
With that caveat in mind, single quote strings should be used by default.

https://www.drupal.org/docs/develop/standards/php/php-coding-standards#:... → .

I've set the status RTBC, does not hurt if anyone else could also check the changes, I'll re-read the changes once more before committing.

This looks good to me as well. Excellent work, @hexaki: thank you very much!

Changed few double quotation marks, but changing all of them would make Elasticsearch tests to fail.

Automatically closed - issue fixed for 2 weeks with no activity.