Pytest, testing expansion for neutrals and plots

[jklenzing]

Description

• Switching from nose to pytest for future unit tests.
  • Adds blank init.py to tests as required by pytest-cov.
  • Switches @raises() to with pytest.raises():
• Other testing expansion
  • Removes python 3.4 from Travis CI testing.
  • Updates handling of plot tests for travis.
  • test_core_class now runs for both the formatted and unformatted test sets.
  • Neutral test data regenerated and tested throughout.
• Fixes bugs in the loading of neutral data into xarray
• Model.plot_lat_alt() now returns figure handle instead of just plotting.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

Tested via Travis CI and locally.

Checklist:

• Make sure you are merging into the develop (not master) branch
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[jklenzing]

Since this test is now run twice and the two data sets are slightly different, updates to use a tolerance rather than exact precision.

[JonathonMSmith]

not sure you need the else here. If reshape is True then the second return will be short-circuited by the return inside the if. But this works just as well. Not sure if there's a benefit one way or the other. Perhaps this is more readable.

[jklenzing]

I was thinking of readability