Commenting: Test code is commented and complex routines sufficiently documented.
PURPOSE file: Test code directory contains a plain text file called PURPOSE which explains what the test addresses along with any other information useful for troubleshooting or understanding it better.
Language-Review: Optional, but preferred: review by someone with language-of-implementation knowledge.
Functional-Review: Optional, but preferred: functionality peer-reviewed (i.e. by someone else) with knowledge of the given domain.