Fixed broken unit test 'test_main.py' and changed test_fuzzy_completion.py to use unittest framework

[geleems]

Fixed broken unit test 'test_main.py'
Failed unit tests in test_main.py:

• test_history_file_not_store_credentials

  • Cause:
    • file_history object does not have append() method but append_string()
    • file_history object is not collection type so len(file_history) fails.

• test_missing_rc_dir

  • Cause:
    • Wong method was used for building filepath --> str(tmpdir.join("subdir").join("rcfile"))

Changed test_fuzzy_completion.py to use unittest framework