v0 of parse tests; minor parse bug fix

[dkain]

Description of proposed changes

What is the goal of this pull request? What does this pull request change?
The goal of this PR is to add some basic testing for parse.py

Related issue(s)

Fixes #
Related to #476

Testing

What steps should be taken to test the changes you've proposed?
If you added or changed behavior in the codebase, did you update the tests, or do you need help with this?

I tested by running the new tests locally. Only codebase modification is reflected / tested int he new tests.

Thank you for contributing to Nextstrain!

[codecov]

Codecov Report

Merging #523 into master will increase coverage by 0.50%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #523      +/-   ##
==========================================
+ Coverage   24.06%   24.57%   +0.50%     
==========================================
  Files          32       32              
  Lines        5156     5156              
  Branches     1298     1298              
==========================================
+ Hits         1241     1267      +26     
+ Misses       3867     3841      -26     
  Partials       48       48              

Impacted Files	Coverage Δ
augur/parse.py	50.00% <100.00%> (+39.39%)	⬆️

---

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 ef91b72...52ee516. Read the comment docs.

[huddlej]

Thank you for the tests and bug fix, @dkain!

I resolved a conflict with master through GitHub's web interface and thought better of this approach after seeing the merge commit it created. I re-resolved the conflict locally, rebased your branch onto master, and pushed PR #573 with these changes.

I'm closing this PR in favor of the new PR with the cleaner version history.