*: extend basic testing chain documentation

[AnnaShaleva]

Save some time for developers who are not familiar with RPC server unit-test structure.

[AliceInHunterland]

Something wrong with the commit.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 83.07%. Comparing base (2b758c5) to head (40dda9f). Report is 2 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #3692 +/- ## ========================================== + Coverage 82.98% 83.07% +0.09% ========================================== Files 335 335 Lines 46708 46708 ========================================== + Hits 38759 38802 +43 + Misses 6360 6318 -42 + Partials 1589 1588 -1 ```

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• Flaky Tests Detection - Detect and resolve failed and flaky tests

[AliceInHunterland]

Maybe a commit length check had been dropped with the new Goland update.

[AnnaShaleva]

Maybe a commit length check had been dropped with the new Goland update.

I don’t use Goland, it’s vim, and it was due to a copy-past. Will fix.