CDRIVER-2432 was resolved in libmongoc 1.10, so it is no longer necessary to use XFAIL in retryable-writes-004.phpt. In fact, the test was only failing because of the manner in which it added a write concern to the findAndModify command. Adding the "writeConcern" directly in the command document instead of using the executeReadWriteCommand() options prevents libmongoc from detecting it. This is irrespective of the fact that the server doesn't actually honor w:0 for a findAndModify command.