Add tests

[ezwelty]

There are currently no tests (!). Here is a basic workflow for addressing that:

• Add Jest
• Use https://github.com/openapi-library/OpenAPIValidators (tutorial: https://dev.to/jameswallis/how-to-use-the-open-api-and-swagger-validator-plugin-for-chai-and-jest-to-keep-your-api-documentation-up-to-date-26om) to test against the OpenAPI spec
• Add additional custom tests