Add tests for buidler cli flags

[cgewecke]

No description provided.

[codecov-io]

Codecov Report

Merging #435 into buidler-plugin will increase coverage by 0.94%.
The diff coverage is 100%.

@@                Coverage Diff                 @@
##           buidler-plugin     #435      +/-   ##
==================================================
+ Coverage           98.26%   99.21%   +0.94%     
==================================================
  Files                  18       18              
  Lines                 750      760      +10     
==================================================
+ Hits                  737      754      +17     
+ Misses                 13        6       -7

Impacted Files	Coverage Δ
dist/plugin-assets/buidler.ui.js	100% <ø> (ø)	⬆️
dist/plugin-assets/plugin.utils.js	97.26% <100%> (-0.04%)	⬇️
dist/truffle.plugin.js	100% <100%> (ø)	⬆️
dist/plugin-assets/buidler.utils.js	100% <100%> (+22.58%)	⬆️
dist/buidler.plugin.js	100% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9d98f3f...f322901. Read the comment docs.