Refactor Collectors to enable Unit Testing

[gfs]

Is your feature request related to a problem? Please describe.
Collectors currently have Functional tests but they do not have unit tests with mocked responses. This means that the collectors are difficult to test in the pipeline (see #735) and are only really tested locally.

Describe the solution you'd like
Refactor collectors so it is possible to mock the many interfaces and libraries they interact with and create unit tests that are safe to run in pipelines.