For update: change the cmdObj for this test case to cmdObj: { update: collName, updates: [{q: {$expr: {$eq: ["$y", "$$myVal"]}}, u: {$set: {z: setFieldVal}}}], let : {myVal: yFieldVal}, }, For delete: change the cmdObj for this test case to cmdObj: { delete: collName, deletes: [{q: {$expr: {$eq: ["$y", "$$myVal"]}}, limit: 1}], let : {myVal: yFieldVal}, }, And they will fail with { "index" : 0, "code" : 17276, "errmsg" : "Write results unavailable from failing to target a host in the shard updateOne_without_shard_key_basic-rs0 :: caused by :: Use of undefined variable: myVal" }