Move tests to groovy spock framework

[ankushkawanpure]

What Changed

• Move tests to groovy spock framework

Why

Issue: https://github.com/graph-quilt/graphql-service-adapters/issues/25

Todo:

• [x] Add tests
• [ ] Add docs

[codecov[bot]]

Codecov Report

Merging #26 (9ce705c) into master (80d1ac1) will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #26   +/-   ##
=========================================
  Coverage     96.05%   96.05%           
  Complexity       21       21           
=========================================
  Files             7        7           
  Lines            76       76           
  Branches          2        2           
=========================================
  Hits             73       73           
  Misses            3        3           

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