There are a number of validate/repair files that are lacking good unit coverage. This ticket will look into adding more unit coverage where possible/appropriate. More information on the existing coverage files can be found by following this guide. Some files of interest include:

mongo/db/catalog/validate_state.cpp

mongo/db/catalog/validate_adaptor.cpp

mongo/db/repair.cpp

mongo/db/catalog/index_repair.cpp

mongo/db/catalog/index_consistency.cpp

Failpoints to look at:

pauseCollectionValidationWithLock
validateCmdCollectionNotValid
crashOnMultikeyValidateFailure