SERVER-125618 added sharding_lag_oplog_application_jscore_passthrough, which runs jstests/core_sharding against a ShardedClusterFixture while LagOplogApplicationInBackground pauses oplog apply on a shard secondary.
That hook does not apply to jstests/sharding, where each test starts its own cluster with ShardingTest.

A hook that introduces the same lag on the replica sets owned by ShardingTest should be added, and then run jstests/sharding under that configuration.