Add error test suites for Buidler plugin

[cgewecke]

No description provided.

[codecov-io]

Codecov Report

Merging #428 into buidler-plugin will increase coverage by 0.26%.
The diff coverage is n/a.

@@                Coverage Diff                 @@
##           buidler-plugin     #428      +/-   ##
==================================================
+ Coverage              98%   98.26%   +0.26%     
==================================================
  Files                  18       18              
  Lines                 750      750              
==================================================
+ Hits                  735      737       +2     
+ Misses                 15       13       -2

Impacted Files	Coverage Δ
dist/buidler.plugin.js	100% <0%> (+3.7%)	⬆️

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