See the comments on the linked BF for more details, but the summary is that `jsTestName()` returns _unknown_name_ when TestData is not set, and in the SELinux evergreen tasks (which do not set TestData), db['__unknown_name__'] is undefined. It seems that tests in jscore don't actually use `jsTestName()` to set the collection they use, but instead will manually namespace a collection that's similar to the name of a test file. This ticket should update validate_datasize.js to behave similarly.

Relevant line: https://github.com/10gen/mongo/blob/9b60d431ed30814490c625c451b5c0e66a28d928/jstests/core/datasize_validation.js?plain=1#L10