Improve test coverage

[tarkatronic]

#164 is now nearly finished; there is only one file left, tests/xpath/00_pathhelper_base.py, and the actual efficacy of the tests is starting to become a little more evident. Overall, they're pretty good, but there definitely needs to be some improvement to help with efforts, such as Python 3 compatibility.

As of now, here is the current coverage of the tests:

Name                            Stmts   Miss Branch BrPart  Cover
-----------------------------------------------------------------
pyangbind/__init__.py               1      0      0      0   100%
pyangbind/helpers/__init__.py       0      0      0      0   100%
pyangbind/helpers/identity.py      95     95     40      0     0%
pyangbind/helpers/misc.py          25     25     16      0     0%
pyangbind/lib/__init__.py           0      0      0      0   100%
pyangbind/lib/base.py              59     12     44     11    76%
pyangbind/lib/pybindJSON.py       105     69     56      5    29%
pyangbind/lib/serialise.py        357     61    270     42    80%
pyangbind/lib/xpathhelper.py      192     26     94     23    83%
pyangbind/lib/yangtypes.py        813     87    378     54    87%
setup.py                           11      0      0      0   100%
-----------------------------------------------------------------
TOTAL                            1658    375    898    135    75%

[tarkatronic]

Codecov is reporting slightly less code coverage. I'm not entirely sure why the discrepancy. But this will give a good ruler for identifying the need here. https://codecov.io/gh/robshakir/pyangbind

[tarkatronic]

I believe this is currently blocked by mbj4668/pyang#325

Due to the way pyang is built, and these tests execute, we are currently unable to measure the coverage of the plugin itself, only the library which gets imported by the generated bindings.

[JoseIgnacioTamayo]

The repo is no longer publishing coverage to CodeCov.

Currently the Test coverage, after running the tests with 'tox' is:

coverage report
Name                            Stmts   Miss Branch BrPart  Cover
-----------------------------------------------------------------
pyangbind/__init__.py               1      0      0      0   100%
pyangbind/helpers/__init__.py       0      0      0      0   100%
pyangbind/helpers/identity.py      97     97     44      0     0%
pyangbind/helpers/misc.py          25     25     16      0     0%
pyangbind/lib/__init__.py           0      0      0      0   100%
pyangbind/lib/base.py              59     12     44     10    77%
pyangbind/lib/pybindJSON.py       103     69     54      4    28%
pyangbind/lib/serialise.py        517     82    338     51    80%
pyangbind/lib/xpathhelper.py      194     26     98     23    83%
pyangbind/lib/yangtypes.py        869     97    394     54    87%
-----------------------------------------------------------------