As part of this test we have 3 nodes in a replica set, and we change the "tags" on two of them. See here.

After switching the tags, we wait for node 2 to acknowledge its new tag, here. We then run some node "targeting" tests, which assume that node 2 is the only node with the closestSecondary tag. However, node 1 may still have this tag, as we haven't waited for it to acknowledge its new tag, fartherSecondary.