Added unit tests for column_type

[vsoulgard]

close #165

[anarthal]

Nothing to object here, thanks. I'll merge once the coverage build finishes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.15%. Comparing base (c20a041) to head (6c0e3e3).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #503   +/-   ##
========================================
  Coverage    99.15%   99.15%           
========================================
  Files          144      144           
  Lines         7370     7370           
========================================
  Hits          7308     7308           
  Misses          62       62           

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c20a041...6c0e3e3. Read the comment docs.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.