Refactor tests

[vjik]

Q	A
Is bugfix?	❌
New feature?	❌
Breaks BC?	❌

Related to yiisoft/db#1098

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.64%. Comparing base (17ddc70) to head (3eaff8a).

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #463   +/-   ##
=========================================
  Coverage     96.64%   96.64%           
  Complexity      408      408           
=========================================
  Files            66       66           
  Lines          1191     1191           
=========================================
  Hits           1151     1151           
  Misses           40       40           

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