Validate JSON schema

[Thomascountz]

When JSON is returned for IBM's Watson Tone Analyzer endpoint, validate the expected JSON schema and return meaningful errors.

This can be achieved using pattern matching

[Thomascountz]

Closes #8

[Thomascountz]

https://github.com/jonasschmidt/ex_json_schema

[Thomascountz]

I'm siding against validating the returned JSON from the Watson API for two reasons,

1) Their endpoints are versionized and their versioning pedagogy is well documented here: https://github.com/watson-developer-cloud/api-guidelines/#versioning. They consider an alteration to the JSON schema to be a breaking change, which would bump the version number.

2) The return structure can vary widely between one key and one value, to two top-level keys with several values, but never is the structure highly nested. At this point, the only validation that could be done is for the key document_tone and tone, all other keys and values returned are dependent on the results of the analysis.

As of version 2017-09-21, {"document_tone":{"tones":[]}} is the minimal return value from Watson for valid requests.

It would be my recommendation- if we believe this feature to provide necessary regression safety- to create a cron job that pings Watson's endpoint and validates the response against a known schema for that request. If this response ever failed validation, alerts could be generated for the development team.

[Thomascountz]

Look into automated contract testing

[Thomascountz]

A private postman monitor has been created to ping Watson's POST endpoint every day at noon. (This monitor is private, because team-level monitors aren't included on the free tier). This monitor runs three tests on two different requests.

• The response status is 200 - The service is up
• The response is JSON
• The response conforms to the expected schema

The schema is validated with the tv4 library, which can be found here: https://github.com/geraintluff/tv4