Write test suite

[jordan-gillard]

I need to preface this issue by saying I love the work you do and that I think this software is very cool.

I notice that this repo doesn't have unit tests. The result of this is that breaking changes and regressions are difficult to catch. I know you guys want to publish EDGAR to pypi, so this is really no bueno. Ideally we'd want a robust test suite that runs in CI for every PR. I think this is especially relevant to PR #10, since it involves major code changes and therefore the strong potential to break existing behavior.

I'm interested in helping Bellingcat, so I'd be happy to work on this or take on an advisory role.