The SERVER-59366 provides basic unit tests, we need integration test with fail injection that makes a health check to be stuck triggering crash in the mongos. We can define a failpoint to stop the HealthObservers from executing checks such that the statistics used by the progress monitor are not updated.

Setup:

• 2 mongos servers
• Workload that performs write operations in a loop

Test:

• Start workload.
• Wait a bit
• Enable the failpoint on one of the mongos processes
• Let FaultManagerConfig::getPeriodicLivenessDeadline elapse while the workload is running
• Observe that operations are redirected to the other mongos
• Observe that writes are accounted for before and after we enabled the failpoint