[Medium Constribution] Add unittests for functions in openupgradelib/openupgrade.py

[bwrsandman]

There are the beginnings of a unittest structure in tests/test_openupgradelib.py

The goal is to increase coverage and guarantee code stability of functions in openupgradelib by:

1. running each function
2. mocking a openerp installation, database, modules
3. checking the calls run on the mocks
4. having a mock database built in travis or in setup
5. checking that openupgradelib correctly manipulates the data

Things to avoid:

1. Implementation tests. This means testing a whole migration at once. A unittest is supposed to test by units. Implementation testing for whole migrations should be done in https://github.com/OCA/openupgrade
2. Using mock to give out the expected answer. Mock should take care of the background details. We don't want to be testing the mock object, we want to test the calls.
3. Testing the best cases. Test edge cases. Example: single id, duplicate ids, no ids, unicode instead of str, None as a parameter.
4. Testing version specific migrations. As said in 1. these scripts should be seen as version agnostic and must be usable for all migrations including non-major migrations.

[pedrobaeza]

I can do it, but I need a first example in which basing my code, because I have never worked with mocks.

[bwrsandman]

Take a look at tests/test_openupgradelib.py It uses Mocks to be able to import openupgrade from openupgradelib.

[bwrsandman]

Done in pedrobaeza#1