Mock testing

[NHDaly]

Set up unit tests that mock out the HTTP responses, so that we can test for specific protocol responses, and ensure we handle all corner cases correctly.

For example, we need to add a unit test that covers the situation in #12, fixed in #13, to ensure it doesn't get broken again in the future.

[billscheidel-rai]

Note: This issue has been migrated to https://relationalai.atlassian.net/browse/RAI-6081.

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