Mapper unit testing: write documentation

[barbarahui]

Tim's mapper unit testing framework needs documentation, especially because it uses pytest in an unconventional way. See Barbara's scratch notes below on what to document.

[barbarahui]

Scratch notes on what to include in documentation:

how to write tests

• base_helper.generate_value_for() -- when would we set the schema type to an actual string value? I guess it might be helpful at some point. Document usage.
• helpers must be named like mappers, but camel case
• general pointers on how to setup a mock request would also be helpful
• explanation of how pytest is being used in an unconventional way, i.e. one test iterates over all mappers. See more detail here.
• how to use cascading merged schemas
  • cascading schemas should mirror the hierarchy of the mappers
  • right now, coverage is in contentdm_helper SCHEMA rather than oai_helper. We should decide what should go where and document that.

how to run tests

We're using pytest, and these are the options you can supply (e.g. pytest metadata_mapper/test/ to run test for all mappers; `pytest metadata_mapper/test/ --mapper=contentdm