In WT-10551 and WT-10626 we're adding testing on the source side for incremental backups. Those tickets are focusing on the changes to each test. I believe there is a common function that all of those tests can/should call. Therefore that code should be in the testutils sources and available to all.

This code, perhaps called testutil_verify_backup_src will verify the bitmap compared to a quiescent copy of the database.

The code needs to do something like this (copied from WT-10626):

• After the child process is killed, the parent should make a copy of the source database directory to a new one, perhaps BACKUP_TEST.
• On the parent, after restart but before verifying the actual data contents, the parent process should get any/all backup IDs and iterate over each ID.
  • For each file, open an incremental backup cursor. For each granularity chunk of the file, if the cursor returns that offset, we need to cmp that chunk from the post-recovery file and the BACKUP_TEST chunk of the file and make sure the contents of the two files are different and if the cursor does NOT return that offset, then the cmp must show that both files are the same for that chunk.