All tests in jstests/core_sharding which run resharding (or resharding-based commands like moveCollection and unshardCollection) are marked with the does_not_support_stepdowns tag (example 1, example 2).

The reason why those tests appear to be prevented from running in step down suites is the following error noting that the timestamp has fallen off the oplog:

"errmsg" : "Recipient shard shard-rs0 reached an unrecoverable error :: caused by :: Executor error during aggregate command on namespace: local.oplog.rs :: caused by :: Specified timestamp has already fallen off the oplog for the input timestamp: [...] 

We should investigate the root cause and adapt the test infrastructure to tolerate stepdowns when resharding to increase test coverage.