This epic will deliver a validate_base stack package that was prototyped in DM-6629 and DM-6917.

• Refactor a new validate_base Stack package (lsst.validate.base) from the existing validate_drp package. validate_base will support a number of validation packages, including validate_drp.
• Implement improvements requested in https://github.com/lsst/validate_drp/pull/21#issuecomment-237342440
• Restore full validate_drp functionality given the new validate_base framework. Including restoration of runtime specification of metric levels and doctests of validation science functions.

Products

• The validate_base API is delivered and includes usability improvements and integration with astropy units for data integrity (follows comments from https://github.com/lsst/validate_drp/pull/21#issuecomment-237342440). Source: https://github.com/lsst/validate_base. (DM-7692, DM-7042)
• A user guide validate_base, currently published at https://validate-base.lsst.io (and will be migrated to https://pipelines.lsst.io). This guide will enable other teams to being to produce QC measurements of their packages. (DM-7042)
• Ported validate_drp to use the validate_base API, including new astropy unit functionality. Also refactored the validate_drp to make it easier to follow calculations, restored ability to select a 'current' specification level, and improved both docstring and README documentation. This code is merged to the u/sqre/measurement-api integration branch pending an RFC to add validate_base as a new dependency of the lsst_qa top-level package. (DM-7933)
• Updated post-qa and released v1.2.0 and v1.2.1 to support valdiate_drp output JSON generated through the new validate_base API. Source at https://github.com/lsst-sqre/post-qa. (DM-6374, DM-7041, DM-8411)