Fix: Split abstract test cases

[localheinz]

This PR

• splits the abstract TestCase into Unit\AbstractTestCase and Integration\AbstractTestCase

[codecov]

Codecov Report

Merging #22 into master will not change coverage by %.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #22   +/-   ##
=========================================
  Coverage     74.22%   74.22%           
  Complexity       80       80           
=========================================
  Files             8        8           
  Lines           194      194           
=========================================
  Hits            144      144           
  Misses           50       50           

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