We've been running with changes to test/checkpoint that michael.cahill added to reproduce data loss issues. These changes are specific to the issue we were investigating and not merge-ready.
We need to take the changes to test/checkpoint files, which can be found in several debug branches, such as:
https://github.com/wiredtiger/wiredtiger/pull/4622/files (A more recent branch)
https://github.com/wiredtiger/wiredtiger/pull/4599/files (Michael's original changes)
and make them able to be merged into the general tree.
This may be controlling them via a command line argument, or copying the test program into another similar, but more specialized version that only runs that version of the code.