Starter Kit: Unit Testing in Open Sentencing

### Background on the problem the feature will solve/improved user experience
Our code currently lacks unit testing, which is needed for test driven development practices: easy debugging, functional testing, etc.

### Describe the solution you'd like
Provide unit tests for various Open Sentencing repositories:

- [ ] https://github.com/Call-for-Code-for-Racial-Justice/Open-Sentencing-UI
- [ ] https://github.com/Call-for-Code-for-Racial-Justice/Open-Sentencing-Aggregator
- [ ] https://github.com/Call-for-Code-for-Racial-Justice/Open-Sentencing-Model

### Tasks
- [ ] research existing tests of similar code bases
- [ ] document list of tests to be implemented for each repository based on programming language, architecture, etc
- [ ] create Github issues for each test in the appropriate repo and link to this issue as well
- [ ] implement changes in each repository as appropriate
- [ ] Add tests for various endpoints
- [ ] Add similar tests for other backend classes and code
- [ ] Add unit tests for front-end functionality

### Acceptance Criteria

- [ ] At least 60% code coverage by unit tests