Added tests in hydra python core.

[farazkhanfk7]

Fixes #

Checklist

• My branch is up-to-date with upstream/develop branch.
• Everything works and tested for Python 3.5.2 and above.

Description

For testing doc_writer we were using unittest’s mock to create mock classes and objects. In that case, we'll have to create mock objects again and again for every test. We can use Pytest’s fixtures to test different components and improve the readability and increase test coverage.

Change logs

• Created conftest.py
• test_doc_writer

  ├── test_context.py   
  ├── test_hydraclass.py   
  ├── test_hydra_collection.py 
  ├── test_hydra_entrypoint    

• Changes in travis.yml and requirements.txt file.