Add rendering tests

[mprins]

• [x] Add some common rendering testcases
• [x] may want to add imagick and/or gd to the CI and composer.json as suggestion
• [x] close #34

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@ba9fdc7). Click here to learn what that means. The diff coverage is n/a.

:exclamation: Current head 7a4340b differs from pull request most recent head 3f76070. Consider uploading reports for the commit 3f76070 to get more accurate results

@@            Coverage Diff            @@
##             master      #41   +/-   ##
=========================================
  Coverage          ?   21.59%           
  Complexity        ?     4293           
=========================================
  Files             ?      180           
  Lines             ?    17779           
  Branches          ?        0           
=========================================
  Hits              ?     3839           
  Misses            ?    13940           
  Partials          ?        0           

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.