Add some unit tests for functions in crash_similarity.py, utils.py and bugzilla.py

[marco-c]

We don't need to write all tests at the same time, there can be multiple PRs where each one adds some tests.

[mansimarkaur]

I'd like to work on this.

[marco-c]

Thanks! You could start with the bugzilla.py module, which is the simplest one.

[mansimarkaur]

How exactly should I be verifying the response for the signatures that returned after a call to get_signatures_from_bug?

[marco-c]

Pick a couple of bugs from bugzilla that have crash signatures, e.g. https://bugzilla.mozilla.org/show_bug.cgi?id=1333486, and verify that the signatures returned by get_signatures_from_bug are the same that you're seeing on Bugzilla ( @0x0 | idmcchandler7_64.dll@0x238bf, @0x0 | idmcchandler7_64.dll@0x1feaf, @0x0 | idmcchandler7_64.dll@0x238bf, etc.).