In my first post on the topic of JSON Schema I outlined the limitations of specifying data-formats by example, described how schema languages help address this, and provided an introduction to the not so well known schema language for JSON – JSON Schema.

In that first article I stated my intention to document non-trivial JSON data-format I specified in the future using JSON Schema in addition to using specification-by-example, whether it be for an API resource or a message payload. When you adhere to this you quickly realise that while producing a JSON Schema is valuable, to increase the value you’ll additionally want to extend the tests for your JSON producing components to automate the following:

• Test the schema remains valid – i.e. it’s well-formed and conforms to the JSON Schema spec.- in order to avoid publishing a broken or invalid schema.
• Test your app produces JSON that conforms to the published schema. This goes beyond just asserting that the component produces an expected lump of JSON, to additionally check that the generated JSON conforms to any validation constraints in the schema.

This follow-up, second post on JSON Schema, provides example code for implementing the above such tests using Java, JUnit and an open-source library for JSON Schema Validation.

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