TST: Fix broken tests failing with 'NoneType' object is not iterable / module 'pandas.util.testing' has no attribute 'assertRaises'

[parthea]

Fixes #57. This 2 line fix was originally part of @tswast's PR #39 but I'm going to transfer it here so that it's easier to capture the specific fix. PR #39 also has other reliability improvements to the integration testing which resolve intermittent failures. The changes in this PR fix the consistent failure TypeError: 'NoneType' object is not iterable.

[codecov-io]

Codecov Report

Merging #58 into master will decrease coverage by 27.76%.
The diff coverage is 0%.

@@             Coverage Diff             @@
##           master      #58       +/-   ##
===========================================
- Coverage   57.04%   29.27%   -27.77%     
===========================================
  Files           4        4               
  Lines        1511     1513        +2     
===========================================
- Hits          862      443      -419     
- Misses        649     1070      +421

Impacted Files	Coverage Δ
pandas_gbq/gbq.py	16.02% <0%> (-40.4%)	⬇️
pandas_gbq/tests/test_gbq.py	31.88% <0%> (-29.99%)	⬇️

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[parthea]

All tests are passing now with the changes in this PR. The majority of the fixes are based on commits from @tswast .
https://travis-ci.org/parthea/pandas-gbq/builds/241645611

[parthea]

Thanks @tswast !

[jreback]

can u add a release note as well

[parthea]

My initial thought is that a release note entry isn't needed because the affected function _Dataset(<project_id>).datasets() at https://github.com/pydata/pandas-gbq/blob/master/pandas_gbq/gbq.py#L1030 is not called in gbq.py. It is only called in integration testing. A release entry is needed if we think someone may be using this specific undocumented function.

[jreback]

@parthea ahh I c. that is all fine. glad tests are passing. thanks!