use REST API mocks in tests

[2bndy5]

Currently, the testing of our REST API calls is lacking because I have not resolved #9

This is a reminder to use a mock library when writing the new tests. The mockito library seems the most popular and well maintained.

[2bndy5]

This might be better implemented in integration tests rather than unit tests. In rust, unit tests are written in private (conditionally compiled) code blocks within the src/ folder. Integration tests are binary executables located in the tests folder.

[2bndy5]

I'm working on this now and found that REST API pagination was not properly implemented. I fixed this locally, but #18 still needs to be addressed as well.