Schema evolution testing

[big-andy-coates]

A big challenge engineers face is knowing if a change they've made to a schema is compatible with previous schema versions, (Most importantly, those schema that exist in prod), and services can work with old data.

Creek should help by testing schema evolution and old data.

Schema evolution checks are possible if we add ability to see older versions of a schema. Simple add a schema resource type. A file in the seed directory could then point to a dir containing the schema. Schema order defined by file name. So simple adding a version into file name orders them, e.g. org.acme.MyType.v3.yml

SR Test extension can then load these in order and fail on incompatible changes.

Old data can be added via existing ability to see data in to Kafka. Need a way of identifying which version of the schema to use to serialise the data... I.e in the record in the seed file.

Can have unit test util that checks latest schema in test resources matches currently generated schema, to ensure schema updates are captured.