test/compatibility provides testing of WT compatibility between MongoDB versions. It basically runs test/format on a base version, then starts a new version and continues running test/format to confirm that WT can continue reading and writing the old data format.

To catch inadvertent format changes (or other incompatibilities) from creeping into WT we should extend test/compatibility so we can do this testing between an pair of git commits. This would let us do things like:

• Test new PRs against the head of develop to make sure they don't break compatibility
• Run nightly tests of compatibility across multiple changes
• Run tests as part of the vendoring process to make sure a batch of changes going into the server don't break compatibility of the previously vendored version of WT.

As part of this ticket, we should decide on where/when we want to do this additional changing and implement that. (Or this could be spun off into a separate ticket.)