Add cli tests

[steven-esser]

Use the scancode cli.py tests as a model. We mainly want to verify correct cli output in certain scenarios.

[johnmhoran]

@MaJuRG Please let me know what you think about my approach in this initial commit. I’ve added three cli tests:

• test_json_output_option_selected()
• test_csv_output_option_selected()
• test_usage_and_help()

To support the cli tests, I’ve copied and slightly modified three functions from scancode/cli_test_utils.py:

• run_scan_click()
• check_json_scan()
• _load_json_result()

I’ve left my comments intact to help explain what I’ve done and pose open questions.

All 130 tests pass, but the return in run_scan_click() raises a warning:

tests/test_cli.py::TestCLI::test_csv_output_option_selected
  C:\code\nexb\dev\deltacode\tests\test_cli.py:62: Warning: Click detected the use of the unicode_literals __future__ import.  This is heavily discouraged because it can introduce subtle bugs in your code.  You should instead use explicit u"" literals for your unicode strings.  For more information see http://click.pocoo.org/python3/
    return runner.invoke(cli.cli, options, catch_exceptions=catch_exceptions)

-- Docs: http://doc.pytest.org/en/latest/warnings.html  

[johnmhoran]

@MaJuRG Is this closer to what you have in mind?

I'm not sure my approach on this line is optimal -- I use a list comprehension but don't really want a list, so I need to grab the item at index 0, which seems a bit convoluted.

I have an idea for a few more tests but welcome your suggestions -- including how we might test for the post-refactoring issues you've run into (you mention them in issue #38).

[steven-esser]

#44 handles the start of this. Closing.