Add test on working without extras

[d-a-bunin]

Before submitting (must do checklist)

• Did you read the contribution guide?
• Did you update the docs? We use Numpy format for all the methods and classes.
• Did you write any new necessary tests?
• Did you update the CHANGELOG?

Proposed Changes

Look #385.

Closing issues

Closes #385.

[github-actions]

🚀 Deployed on https://deploy-preview-463--etna-docs.netlify.app

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.41%. Comparing base (ee7fca9) to head (5753fa7).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #463   +/-   ##
=======================================
  Coverage   90.41%   90.41%           
=======================================
  Files         229      229           
  Lines       15940    15940           
=======================================
  Hits        14412    14412           
  Misses       1528     1528           

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