It'd be nice to use codecov.io to validate whether or not some part of the codebase is getting tested. Though our code coverage tasks indicate that uploading is succeeding, codecov.io does not show lines run.

For example: https://codecov.io/gh/mongodb/mongo-c-driver/src/master/src/libmongoc/src/mongoc/mongoc-aggregate.c
Just shows the file, but does not highlight the lines run.