SERVER-43749 Modernize mapReduce tests in core

27 files changed, 316 insertions, 764 deletions

diff --git a/buildscripts/resmokeconfig/suites/causally_consistent_jscore_passthrough.yml b/buildscripts/resmokeconfig/suites/causally_consistent_jscore_passthrough.yml
index 35069ac7c3b..55a20cee7f2 100644
--- a/buildscripts/resmokeconfig/suites/causally_consistent_jscore_passthrough.yml
+++ b/buildscripts/resmokeconfig/suites/causally_consistent_jscore_passthrough.yml
@@ -51,8 +51,6 @@ selector:
   - jstests/core/stages_delete.js # Uses stageDebug command for deletes.
   # Tests that fail for Causal Consistency as they have statements that do not support
   # non-local read concern.
-  - jstests/core/geo_mapreduce.js
-  - jstests/core/geo_mapreduce2.js
   - jstests/core/geo_big_polygon3.js
   - jstests/core/mr*.js
   - jstests/core/collation.js
diff --git a/buildscripts/resmokeconfig/suites/causally_consistent_jscore_passthrough_auth.yml b/buildscripts/resmokeconfig/suites/causally_consistent_jscore_passthrough_auth.yml
index bf21865b3be..c13ffe4142e 100644
--- a/buildscripts/resmokeconfig/suites/causally_consistent_jscore_passthrough_auth.yml
+++ b/buildscripts/resmokeconfig/suites/causally_consistent_jscore_passthrough_auth.yml
@@ -63,8 +63,6 @@ selector:
   - jstests/core/stages_delete.js # Uses stageDebug command for deletes.
   # Tests that fail for Causal Consistency as they have statements that do not support
   # non-local read concern.
-  - jstests/core/geo_mapreduce.js
-  - jstests/core/geo_mapreduce2.js
   - jstests/core/geo_big_polygon3.js
   - jstests/core/mr*.js
   - jstests/core/collation.js
diff --git a/buildscripts/resmokeconfig/suites/core_map_reduce_agg.yaml b/buildscripts/resmokeconfig/suites/core_map_reduce_agg.yaml
index d7aee4d28ea..34f9f15fb35 100644
--- a/buildscripts/resmokeconfig/suites/core_map_reduce_agg.yaml
+++ b/buildscripts/resmokeconfig/suites/core_map_reduce_agg.yaml
@@ -7,14 +7,12 @@ selector:
   - jstests/core/commands_namespace_parsing.js
   - jstests/core/map_reduce_validation.js
   - jstests/core/mr_preserve_indexes.js
-  - jstests/core/mr_merge2.js
+  - jstests/core/mr_merge.js
   - jstests/core/mr_mutable_properties.js
-  - jstests/core/mr_outreduce.js
-  - jstests/core/mr_outreduce2.js
+  - jstests/core/mr_reduce.js
   - jstests/core/mr_sort.js
   - jstests/core/mr_stored.js
   - jstests/core/mr_tolerates_js_exception.js
-  - jstests/core/mr_undef.js
   - jstests/core/mr_use_this_object.js
   - jstests/core/mr_scope.js
   - jstests/core/profile_mapreduce.js
diff --git a/buildscripts/resmokeconfig/suites/logical_session_cache_sharding_100ms_refresh_jscore_passthrough.yml b/buildscripts/resmokeconfig/suites/logical_session_cache_sharding_100ms_refresh_jscore_passthrough.yml
index bc6291f3fda..df1d2b5e692 100644
--- a/buildscripts/resmokeconfig/suites/logical_session_cache_sharding_100ms_refresh_jscore_passthrough.yml
+++ b/buildscripts/resmokeconfig/suites/logical_session_cache_sharding_100ms_refresh_jscore_passthrough.yml
@@ -81,9 +81,8 @@ selector:
   # TODO: Remove after fixing SERVER-32563. The implementation of explain for the count command is
   # incorrect on sharded collections.
   - jstests/core/explain_count.js
-  # TODO: Remove after fixing SERVER-14324. mapReduce behaves unpredictably when the out collection
-  # is sharded on anything other than {_id: 1}.
-  - jstests/core/mr_undef.js
+  # TODO: Remove after implementing SERVER-42677. Legacy mapReduce behaves unpredictably when the
+  # out collection is sharded on anything other than {_id: 1}.
   # TODO SERVER-32311: These tests use plan stage helpers which can't handle sharded explain output.
   - jstests/core/expr_index_use.js
   - jstests/core/index_multikey.js
diff --git a/buildscripts/resmokeconfig/suites/logical_session_cache_sharding_10sec_refresh_jscore_passthrough.yml b/buildscripts/resmokeconfig/suites/logical_session_cache_sharding_10sec_refresh_jscore_passthrough.yml
index 690a2bd9a4f..deae692c9d3 100644
--- a/buildscripts/resmokeconfig/suites/logical_session_cache_sharding_10sec_refresh_jscore_passthrough.yml
+++ b/buildscripts/resmokeconfig/suites/logical_session_cache_sharding_10sec_refresh_jscore_passthrough.yml
@@ -81,9 +81,8 @@ selector:
   # TODO: Remove after fixing SERVER-32563. The implementation of explain for the count command is
   # incorrect on sharded collections.
   - jstests/core/explain_count.js
-  # TODO: Remove after fixing SERVER-14324. mapReduce behaves unpredictably when the out collection
-  # is sharded on anything other than {_id: 1}.
-  - jstests/core/mr_undef.js
+  # TODO: Remove after implementing SERVER-42677. Legacy mapReduce behaves unpredictably when the
+  # out collection is sharded on anything other than {_id: 1}.
   # TODO SERVER-32311: These tests use plan stage helpers which can't handle sharded explain output.
   - jstests/core/expr_index_use.js
   - jstests/core/index_multikey.js
diff --git a/buildscripts/resmokeconfig/suites/logical_session_cache_sharding_1sec_refresh_jscore_passthrough.yml b/buildscripts/resmokeconfig/suites/logical_session_cache_sharding_1sec_refresh_jscore_passthrough.yml
index b3e3966a394..e9095451da0 100644
--- a/buildscripts/resmokeconfig/suites/logical_session_cache_sharding_1sec_refresh_jscore_passthrough.yml
+++ b/buildscripts/resmokeconfig/suites/logical_session_cache_sharding_1sec_refresh_jscore_passthrough.yml
@@ -81,9 +81,8 @@ selector:
   # TODO: Remove after fixing SERVER-32563. The implementation of explain for the count command is
   # incorrect on sharded collections.
   - jstests/core/explain_count.js
-  # TODO: Remove after fixing SERVER-14324. mapReduce behaves unpredictably when the out collection
-  # is sharded on anything other than {_id: 1}.
-  - jstests/core/mr_undef.js
+  # TODO: Remove after implementing SERVER-42677. Legacy mapReduce behaves unpredictably when the
+  # out collection is sharded on anything other than {_id: 1}.
   # TODO SERVER-32311: These tests use plan stage helpers which can't handle sharded explain output.
   - jstests/core/expr_index_use.js
   - jstests/core/index_multikey.js
diff --git a/buildscripts/resmokeconfig/suites/logical_session_cache_sharding_default_refresh_jscore_passthrough.yml b/buildscripts/resmokeconfig/suites/logical_session_cache_sharding_default_refresh_jscore_passthrough.yml
index dbd0948dac7..34bfad07835 100644
--- a/buildscripts/resmokeconfig/suites/logical_session_cache_sharding_default_refresh_jscore_passthrough.yml
+++ b/buildscripts/resmokeconfig/suites/logical_session_cache_sharding_default_refresh_jscore_passthrough.yml
@@ -81,9 +81,8 @@ selector:
   # TODO: Remove after fixing SERVER-32563. The implementation of explain for the count command is
   # incorrect on sharded collections.
   - jstests/core/explain_count.js
-  # TODO: Remove after fixing SERVER-14324. mapReduce behaves unpredictably when the out collection
-  # is sharded on anything other than {_id: 1}.
-  - jstests/core/mr_undef.js
+  # TODO: Remove after implementing SERVER-42677. Legacy mapReduce behaves unpredictably when the
+  # out collection is sharded on anything other than {_id: 1}.
   # TODO SERVER-32311: These tests use plan stage helpers which can't handle sharded explain output.
   - jstests/core/expr_index_use.js
   - jstests/core/index_multikey.js
diff --git a/buildscripts/resmokeconfig/suites/multi_shard_local_read_write_multi_stmt_txn_jscore_passthrough.yml b/buildscripts/resmokeconfig/suites/multi_shard_local_read_write_multi_stmt_txn_jscore_passthrough.yml
index 2543d348ccd..cf7102b299c 100644
--- a/buildscripts/resmokeconfig/suites/multi_shard_local_read_write_multi_stmt_txn_jscore_passthrough.yml
+++ b/buildscripts/resmokeconfig/suites/multi_shard_local_read_write_multi_stmt_txn_jscore_passthrough.yml
@@ -76,9 +76,8 @@ selector:
   # TODO: Remove after fixing SERVER-32563. The implementation of explain for the count command is
   # incorrect on sharded collections.
   - jstests/core/explain_count.js
-  # TODO: Remove after fixing SERVER-14324. mapReduce behaves unpredictably when the out collection
-  # is sharded on anything other than {_id: 1}.
-  - jstests/core/mr_undef.js
+  # TODO: Remove after implementing SERVER-42677. Legacy mapReduce behaves unpredictably when the
+  # out collection is sharded on anything other than {_id: 1}.
   # TODO SERVER-32311: These tests use plan stage helpers which can't handle sharded explain output.
   - jstests/core/expr_index_use.js
   - jstests/core/index_multikey.js
diff --git a/buildscripts/resmokeconfig/suites/multi_shard_multi_stmt_txn_jscore_passthrough.yml b/buildscripts/resmokeconfig/suites/multi_shard_multi_stmt_txn_jscore_passthrough.yml
index 42576d1e2d6..b18dffb9ae9 100644
--- a/buildscripts/resmokeconfig/suites/multi_shard_multi_stmt_txn_jscore_passthrough.yml
+++ b/buildscripts/resmokeconfig/suites/multi_shard_multi_stmt_txn_jscore_passthrough.yml
@@ -76,9 +76,8 @@ selector:
   # TODO: Remove after fixing SERVER-32563. The implementation of explain for the count command is
   # incorrect on sharded collections.
   - jstests/core/explain_count.js
-  # TODO: Remove after fixing SERVER-14324. mapReduce behaves unpredictably when the out collection
-  # is sharded on anything other than {_id: 1}.
-  - jstests/core/mr_undef.js
+  # TODO: Remove after implementing SERVER-42677. Legacy mapReduce behaves unpredictably when the
+  # out collection is sharded on anything other than {_id: 1}.
   # TODO SERVER-32311: These tests use plan stage helpers which can't handle sharded explain output.
   - jstests/core/expr_index_use.js
   - jstests/core/index_multikey.js
diff --git a/buildscripts/resmokeconfig/suites/multi_shard_multi_stmt_txn_kill_primary_jscore_passthrough.yml b/buildscripts/resmokeconfig/suites/multi_shard_multi_stmt_txn_kill_primary_jscore_passthrough.yml
index a683683967b..12fce0cf58f 100644
--- a/buildscripts/resmokeconfig/suites/multi_shard_multi_stmt_txn_kill_primary_jscore_passthrough.yml
+++ b/buildscripts/resmokeconfig/suites/multi_shard_multi_stmt_txn_kill_primary_jscore_passthrough.yml
@@ -76,9 +76,8 @@ selector:
   # TODO: Remove after fixing SERVER-32563. The implementation of explain for the count command is
   # incorrect on sharded collections.
   - jstests/core/explain_count.js
-  # TODO: Remove after fixing SERVER-14324. mapReduce behaves unpredictably when the out collection
-  # is sharded on anything other than {_id: 1}.
-  - jstests/core/mr_undef.js
+  # TODO: Remove after implementing SERVER-42677. Legacy mapReduce behaves unpredictably when the
+  # out collection is sharded on anything other than {_id: 1}.
   # TODO SERVER-32311: These tests use plan stage helpers which can't handle sharded explain output.
   - jstests/core/expr_index_use.js
   - jstests/core/index_multikey.js
diff --git a/buildscripts/resmokeconfig/suites/multi_shard_multi_stmt_txn_stepdown_primary_jscore_passthrough.yml b/buildscripts/resmokeconfig/suites/multi_shard_multi_stmt_txn_stepdown_primary_jscore_passthrough.yml
index 7c2cf72f810..a71ae52e23e 100644
--- a/buildscripts/resmokeconfig/suites/multi_shard_multi_stmt_txn_stepdown_primary_jscore_passthrough.yml
+++ b/buildscripts/resmokeconfig/suites/multi_shard_multi_stmt_txn_stepdown_primary_jscore_passthrough.yml
@@ -76,9 +76,8 @@ selector:
   # TODO: Remove after fixing SERVER-32563. The implementation of explain for the count command is
   # incorrect on sharded collections.
   - jstests/core/explain_count.js
-  # TODO: Remove after fixing SERVER-14324. mapReduce behaves unpredictably when the out collection
-  # is sharded on anything other than {_id: 1}.
-  - jstests/core/mr_undef.js
+  # TODO: Remove after implementing SERVER-42677. Legacy mapReduce behaves unpredictably when the
+  # out collection is sharded on anything other than {_id: 1}.
   # TODO SERVER-32311: These tests use plan stage helpers which can't handle sharded explain output.
   - jstests/core/expr_index_use.js
   - jstests/core/index_multikey.js
@@ -157,7 +156,6 @@ selector:
   # txn_passthrough_cmd_massage.js ineffective for preventing 2 phase drops
   # from contesting db/coll locks.
   - jstests/core/function_string_representations.js
-  - jstests/core/geo_mapreduce2.js
   - jstests/core/mr*.js
   - jstests/core/or4.js
 
diff --git a/buildscripts/resmokeconfig/suites/multi_stmt_txn_jscore_passthrough_with_migration.yml b/buildscripts/resmokeconfig/suites/multi_stmt_txn_jscore_passthrough_with_migration.yml
index f546198a39e..a7825009894 100644
--- a/buildscripts/resmokeconfig/suites/multi_stmt_txn_jscore_passthrough_with_migration.yml
+++ b/buildscripts/resmokeconfig/suites/multi_stmt_txn_jscore_passthrough_with_migration.yml
@@ -76,9 +76,8 @@ selector:
   # TODO: Remove after fixing SERVER-32563. The implementation of explain for the count command is
   # incorrect on sharded collections.
   - jstests/core/explain_count.js
-  # TODO: Remove after fixing SERVER-14324. mapReduce behaves unpredictably when the out collection
-  # is sharded on anything other than {_id: 1}.
-  - jstests/core/mr_undef.js
+  # TODO: Remove after implementing SERVER-42677. Legacy mapReduce behaves unpredictably when the
+  # out collection is sharded on anything other than {_id: 1}.
   # TODO SERVER-32311: These tests use plan stage helpers which can't handle sharded explain output.
   - jstests/core/expr_index_use.js
   - jstests/core/index_multikey.js
diff --git a/buildscripts/resmokeconfig/suites/sharded_causally_consistent_jscore_passthrough.yml b/buildscripts/resmokeconfig/suites/sharded_causally_consistent_jscore_passthrough.yml
index 19d8d1feb7c..2f964f507c9 100644
--- a/buildscripts/resmokeconfig/suites/sharded_causally_consistent_jscore_passthrough.yml
+++ b/buildscripts/resmokeconfig/suites/sharded_causally_consistent_jscore_passthrough.yml
@@ -65,7 +65,6 @@ selector:
   - jstests/core/mr_correctness.js
   - jstests/core/mr_fail_invalid_js.js
   - jstests/core/mr_scope.js
-  - jstests/core/mr_undef.js
   # TODO: SERVER-30052
   - jstests/core/queryoptimizer3.js
   # TODO: SERVER-27269: mongos can't establish cursor if view has $collStats and views another view.
@@ -75,8 +74,6 @@ selector:
   - jstests/core/stages_delete.js # Uses stageDebug command for deletes.
   # Tests that fail for Causal Consistency as they have statements that do not support
   # non-local read concern.
-  - jstests/core/geo_mapreduce.js
-  - jstests/core/geo_mapreduce2.js
   - jstests/core/geo_big_polygon3.js
   - jstests/core/mr*.js
   - jstests/core/collation.js
diff --git a/buildscripts/resmokeconfig/suites/sharded_collections_jscore_passthrough.yml b/buildscripts/resmokeconfig/suites/sharded_collections_jscore_passthrough.yml
index 3f482a91acc..03e971ca184 100644
--- a/buildscripts/resmokeconfig/suites/sharded_collections_jscore_passthrough.yml
+++ b/buildscripts/resmokeconfig/suites/sharded_collections_jscore_passthrough.yml
@@ -76,9 +76,8 @@ selector:
   # TODO: Remove after fixing SERVER-32563. The implementation of explain for the count command is
   # incorrect on sharded collections.
   - jstests/core/explain_count.js
-  # TODO: Remove after fixing SERVER-14324. mapReduce behaves unpredictably when the out collection
-  # is sharded on anything other than {_id: 1}.
-  - jstests/core/mr_undef.js
+  # TODO: Remove after implementing SERVER-42677. Legacy mapReduce behaves unpredictably when the
+  # out collection is sharded on anything other than {_id: 1}.
   # TODO SERVER-32311: These tests use plan stage helpers which can't handle sharded explain output.
   - jstests/core/expr_index_use.js
   - jstests/core/index_multikey.js
diff --git a/jstests/aggregation/extras/mrabench.js b/jstests/aggregation/extras/mrabench.js
deleted file mode 100644
index 78be64a2064..00000000000
--- a/jstests/aggregation/extras/mrabench.js
+++ /dev/null
@@ -1,50 +0,0 @@
-/*
-  In order to run this, you need to have a local copy of the usage data.
-
-  One way to do this is to dump and restore it using mongodump and mongorestore
-  */
-
-db = db.getSiblingDB("mongousage");
-
-function rollupMap() {
-    emit(this._id.t, {total: this.value, unique: 1});
-}
-
-function rollupReduce(key, values) {
-    var res = {total: 0, unique: 0};
-    for (var i = 0; i < values.length; i++) {
-        res.total += values[i].total;
-        res.unique += values[i].unique;
-    }
-    return res;
-}
-
-function mrrollups() {
-    res = db.gen.monthly.ip.mapReduce(rollupMap, rollupReduce, {out: "gen.monthly"});
-    res.find().sort({_id: -1}).forEach(printjsononeline);
-
-    res = db.gen.weekly.ip.mapReduce(rollupMap, rollupReduce, {out: "gen.weekly"});
-    res.find().sort({_id: -1}).forEach(printjsononeline);
-}
-
-function rollupMonthlyMR() {
-    resMonthlyMR = db.gen.monthly.ip.mapReduce(rollupMap, rollupReduce, {out: {inline: 1}});
-}
-
-function rollupWeeklyMR() {
-    resWeeklyMR = db.gen.weekly.ip.mapReduce(rollupMap, rollupReduce, {out: {inline: 1}});
-}
-
-function rollupMonthlyA() {
-    resMonthlyA = db.runCommand({
-        aggregate: "gen.monthly.ip",
-        pipeline: [{$group: {_id: {month: "_id.t"}, total: {$sum: "$value"}, unique: {$sum: 1}}}]
-    });
-}
-
-function rollupWeeklyA() {
-    resWeeklyA = db.runCommand({
-        aggregate: "gen.weekly.ip",
-        pipeline: [{$group: {_id: {month: "_id.t"}, total: {$sum: "$value"}, unique: {$sum: 1}}}]
-    });
-}
diff --git a/jstests/core/geo_mapreduce.js b/jstests/core/geo_mapreduce.js
deleted file mode 100644
index 8bf93d7fd81..00000000000
--- a/jstests/core/geo_mapreduce.js
+++ /dev/null
@@ -1,64 +0,0 @@
-// @tags: [
-//   # mapReduce does not support afterClusterTime.
-//   does_not_support_causal_consistency,
-//   does_not_support_stepdowns,
-// ]
-
-// Test script from SERVER-1742
-
-// MongoDB test script for mapreduce with geo query
-
-// setup test collection
-db.apples.drop();
-db.apples.insert({"geo": {"lat": 32.68331909, "long": 69.41610718}, "apples": 5});
-db.apples.insert({"geo": {"lat": 35.01860809, "long": 70.92027283}, "apples": 2});
-db.apples.insert({"geo": {"lat": 31.11639023, "long": 64.19970703}, "apples": 11});
-db.apples.insert({"geo": {"lat": 32.64500046, "long": 69.36251068}, "apples": 4});
-db.apples.insert({"geo": {"lat": 33.23638916, "long": 69.81360626}, "apples": 9});
-db.apples.ensureIndex({"geo": "2d"});
-
-center = [32.68, 69.41];
-radius = 10 / 111;  // 10km; 1 arcdegree ~= 111km
-geo_query = {
-    geo: {'$within': {'$center': [center, radius]}}
-};
-
-// geo query on collection works fine
-res = db.apples.find(geo_query);
-assert.eq(2, res.count());
-
-// map function
-m = function() {
-    emit(null, {"apples": this.apples});
-};
-
-// reduce function
-r = function(key, values) {
-    var total = 0;
-    for (var i = 0; i < values.length; i++) {
-        total += values[i].apples;
-    }
-    return {"apples": total};
-};
-
-// mapreduce without geo query works fine
-res = db.apples.mapReduce(m, r, {out: {inline: 1}});
-
-printjson(res);
-total = res.results[0];
-assert.eq(31, total.value.apples);
-
-// mapreduce with regular query works fine too
-res = db.apples.mapReduce(m, r, {out: {inline: 1}, query: {apples: {'$lt': 9}}});
-total = res.results[0];
-assert.eq(11, total.value.apples);
-
-// mapreduce with geo query gives error on mongodb version 1.6.2
-// uncaught exception: map reduce failed: {
-// "assertion" : "manual matcher config not allowed",
-// "assertionCode" : 13285,
-// "errmsg" : "db assertion failure",
-// "ok" : 0 }
-res = db.apples.mapReduce(m, r, {out: {inline: 1}, query: geo_query});
-total = res.results[0];
-assert.eq(9, total.value.apples);
diff --git a/jstests/core/geo_mapreduce2.js b/jstests/core/geo_mapreduce2.js
deleted file mode 100644
index a740e723101..00000000000
--- a/jstests/core/geo_mapreduce2.js
+++ /dev/null
@@ -1,43 +0,0 @@
-// @tags: [
-//   # mapReduce does not support afterClusterTime.
-//   does_not_support_causal_consistency,
-//   does_not_support_stepdowns,
-//   uses_map_reduce_with_temp_collections,
-// ]
-
-// Geo mapreduce 2 from SERVER-3478
-
-var coll = db.geoMR2;
-coll.drop();
-
-for (var i = 0; i < 300; i++)
-    coll.insert({i: i, location: [10, 20]});
-
-coll.ensureIndex({location: "2d"});
-
-// map function
-m = function() {
-    emit(null, {count: this.i});
-};
-
-// reduce function
-r = function(key, values) {
-    var total = 0;
-    for (var i = 0; i < values.length; i++) {
-        total += values[i].count;
-    }
-
-    return {count: total};
-};
-
-try {
-    coll.mapReduce(m, r, {
-        out: coll.getName() + "_mr",
-        sort: {_id: 1},
-        query: {'location': {$within: {$centerSphere: [[10, 20], 0.01]}}}
-    });
-
-} catch (e) {
-    // This should occur, since we can't in-mem sort for mreduce
-    printjson(e);
-}
diff --git a/jstests/core/mr_killop.js b/jstests/core/mr_killop.js
index 6c837c52943..07a92e289eb 100644
--- a/jstests/core/mr_killop.js
+++ b/jstests/core/mr_killop.js
@@ -1,3 +1,4 @@
+// Test killop applied to m/r operations and child ops of m/r operations.
 // Cannot implicitly shard accessed collections because the "command" field in the currentOp()
 // output is reported as {"mapreduce.shardedfinish": { mapreduce: "jstests_mr_killop", ... }, ... }
 // when the "finalize" option to the "mapReduce" command is used on a sharded collection.
@@ -9,77 +10,54 @@
 //   uses_multiple_connections,
 //   uses_map_reduce_with_temp_collections,
 // ]
-
-// Test killop applied to m/r operations and child ops of m/r operations.
-
-t = db.jstests_mr_killop;
-t.drop();
-t2 = db.jstests_mr_killop_out;
-t2.drop();
-db.adminCommand({"configureFailPoint": 'mr_killop_test_fp', "mode": 'alwaysOn'});
-function debug(x) {
-    //        printjson( x );
-}
-
-/** @return op code for map reduce op created by spawned shell, or that op's child */
-function op(childLoop) {
-    p = db.currentOp().inprog;
-    debug(p);
-
-    let isMapReduce = function(op) {
+(function() {
+"use strict";
+const source = db.jstests_mr_killop;
+source.drop();
+const out = db.jstests_mr_killop_out;
+out.drop();
+assert.commandWorked(db.adminCommand({configureFailPoint: "mr_killop_test_fp", mode: "alwaysOn"}));
+
+/** @return op code for map reduce op created by spawned shell. */
+function getOpCode() {
+    const inProg = db.currentOp().inprog;
+
+    function isMapReduce(op) {
         if (!op.command) {
             return false;
         }
 
-        let cmdBody = op.command;
+        const cmdBody = op.command;
         if (cmdBody.$truncated) {
-            let stringifiedCmd = cmdBody.$truncated;
-            print('str: ' + tojson(stringifiedCmd));
+            const stringifiedCmd = cmdBody.$truncated;
             return stringifiedCmd.search('mapreduce') >= 0 &&
-                stringifiedCmd.search('jstests_mr_killop') >= 0;
+                stringifiedCmd.search(source.getName()) >= 0;
         }
 
-        return cmdBody.mapreduce && cmdBody.mapreduce == "jstests_mr_killop";
-    };
-
-    for (var i in p) {
-        var o = p[i];
-        // Identify a map/reduce or where distinct operation by its collection, whether or not
-        // it is currently active.
-        if (childLoop) {
-            if ((o.active || o.waitingForLock) && o.command && o.command.query &&
-                o.command.query.$where && o.command.distinct == "jstests_mr_killop") {
-                return o.opid;
-            }
-        } else {
-            if ((o.active || o.waitingForLock) && isMapReduce(o)) {
-                return o.opid;
-            }
-        }
+        return cmdBody.mapreduce && cmdBody.mapreduce == source.getName();
+    }
+
+    for (let i in inProg) {
+        const o = inProg[i];
+        // Identify a map/reduce operation by its collection, whether or not it is currently active.
+        if ((o.active || o.waitingForLock) && isMapReduce(o))
+            return o.opid;
     }
     return -1;
 }
 
 /**
- * Run one map reduce with the specified parameters in a parallel shell, kill the
- * map reduce op or its child op with killOp, and wait for the map reduce op to
- * terminate.
- * @param childLoop - if true, a distinct $where op is killed rather than the map reduce op.
- * This is necessay for a child distinct $where of a map reduce op because child
- * ops currently mask parent ops in currentOp.
+ * Run one mapReduce with the specified parameters in a parallel shell. Kill the map reduce op and
+ * wait for the map reduce op to terminate.
  */
-function testOne(map, reduce, finalize, scope, childLoop, wait) {
-    debug("testOne - map = " + tojson(map) + "; reduce = " + tojson(reduce) +
-          "; finalize = " + tojson(finalize) + "; scope = " + tojson(scope) +
-          "; childLoop = " + childLoop + "; wait = " + wait);
-
-    t.drop();
-    t2.drop();
-    // Ensure we have 2 documents for the reduce to run
-    t.save({a: 1});
-    t.save({a: 1});
-
-    spec = {mapreduce: "jstests_mr_killop", out: "jstests_mr_killop_out", map: map, reduce: reduce};
+function runTest(map, reduce, finalize, scope, wait) {
+    source.drop();
+    out.drop();
+    // Ensure we have 2 documents for the reduce to run.
+    assert.commandWorked(source.insert({a: 1}));
+    assert.commandWorked(source.insert({a: 1}));
+
+    const spec = {mapreduce: source.getName(), out: out.getName(), map: map, reduce: reduce};
     if (finalize) {
         spec["finalize"] = finalize;
     }
@@ -87,85 +65,94 @@ function testOne(map, reduce, finalize, scope, childLoop, wait) {
         spec["scope"] = scope;
     }
 
-    // Windows shell strips all double quotes from command line, so use
-    // single quotes.
-    stringifiedSpec = tojson(spec).toString().replace(/\n/g, ' ').replace(/\"/g, "\'");
+    // Windows shell strips all double quotes from command line, so use single quotes.
+    const stringifiedSpec = tojson(spec).toString().replace(/\n/g, ' ').replace(/\"/g, "\'");
 
-    // The assert below won't be caught by this test script, but it will cause error messages
-    // to be printed.
-    var awaitShell =
+    // The assert below won't be caught by this test script, but it will cause error messages to be
+    // printed.
+    const awaitShell =
         startParallelShell("assert.commandWorked( db.runCommand( " + stringifiedSpec + " ) );");
 
     if (wait) {
         sleep(2000);
     }
 
-    o = null;
+    let opCode = null;
     assert.soon(function() {
-        o = op(childLoop);
-        return o != -1;
+        opCode = getOpCode();
+        return opCode != -1;
     });
 
-    res = db.killOp(o);
-    debug("did kill : " + tojson(res));
+    db.killOp(opCode);
 
     // When the map reduce op is killed, the spawned shell will exit
-    var exitCode = awaitShell({checkExitSuccess: false});
+    const exitCode = awaitShell({checkExitSuccess: false});
     assert.neq(0,
                exitCode,
                "expected shell to exit abnormally due to map-reduce execution being terminated");
-    debug("parallel shell completed");
+    assert.eq(-1, getOpCode());
+}
 
-    assert.eq(-1, op(childLoop));
+/** Test using wait and non wait modes. */
+function runTests(map, reduce, finalize, scope) {
+    runTest(map, reduce, finalize, scope, false);
+    runTest(map, reduce, finalize, scope, true);
 }
 
-/** Test using wait and non wait modes */
-function test(map, reduce, finalize, scope, childLoop) {
-    debug(" Non wait mode");
-    testOne(map, reduce, finalize, scope, childLoop, false);
+/** Test looping in map function. */
+function runMapTests(loop) {
+    // Without scope.
+    runTests(
+        loop,  // map
+        function(k, v) {
+            return v[0];
+        },     // reduce
+        null,  // finalize
+        null   // scope
+    );
 
-    debug(" Wait mode");
-    testOne(map, reduce, finalize, scope, childLoop, true);
+    // With scope.
+    runTests(
+        function() {
+            loop();
+        },  // map
+        function(k, v) {
+            return v[0];
+        },            // reduce
+        null,         // finalize
+        {loop: loop}  // scope
+    );
 }
 
-/** Test looping in map and reduce functions */
-function runMRTests(loop, childLoop) {
-    debug(" Running MR test - loop map function. no scope ");
-    test(loop,  // map
-         function(k, v) {
-             return v[0];
-         },     // reduce
-         null,  // finalize
-         null,  // scope
-         childLoop);
-
-    debug(" Running MR test - loop reduce function ");
-    test(
+/** Test looping in reduce function. */
+function runReduceTests(loop) {
+    // Without scope.
+    runTests(
         function() {
             emit(this.a, 1);
         },     // map
         loop,  // reduce
         null,  // finalize
-        null,  // scope
-        childLoop);
+        null   // scope
+    );
 
-    debug(" Running finalization test - loop map function. with scope ");
-    test(
+    // With scope.
+    runTests(
         function() {
-            loop();
+            emit(this.a, 1);
         },  // map
-        function(k, v) {
-            return v[0];
-        },             // reduce
-        null,          // finalize
-        {loop: loop},  // scope
-        childLoop);
+        function() {
+            loop();
+        },            // reduce
+        null,         // finalize
+        {loop: loop}  // scope
+    );
 }
 
-/** Test looping in finalize function */
-function runFinalizeTests(loop, childLoop) {
-    debug(" Running finalization test - no scope ");
-    test(
+/** Test looping in finalize function. */
+function runFinalizeTests(loop) {
+    // Without scope.
+    runTests(
         function() {
             emit(this.a, 1);
         },  // map
@@ -173,11 +160,11 @@ function runFinalizeTests(loop, childLoop) {
             return v[0];
         },     // reduce
         loop,  // finalize
-        null,  // scope
-        childLoop);
+        null   // scope
+    );
 
-    debug(" Running finalization test - with scope ");
-    test(
+    // With scope.
+    runTests(
         function() {
             emit(this.a, 1);
         },  // map
@@ -186,17 +173,18 @@ function runFinalizeTests(loop, childLoop) {
         },  // reduce
         function(a, b) {
             loop();
-        },             // finalize
-        {loop: loop},  // scope
-        childLoop);
+        },            // finalize
+        {loop: loop}  // scope
+    );
 }
 
-// Run inside server. No access to debug().
-var loop = function() {
+const loop = function() {
     while (1) {
         sleep(1000);
     }
 };
-runMRTests(loop, false);
+runMapTests(loop, false);
+runReduceTests(loop, false);
 runFinalizeTests(loop, false);
-db.adminCommand({"configureFailPoint": 'mr_killop_test_fp', "mode": 'off'});
+db.adminCommand({configureFailPoint: "mr_killop_test_fp", mode: "off"});
+}());
diff --git a/jstests/core/mr_merge.js b/jstests/core/mr_merge.js
index 835cee55c27..fa9d2c3d873 100644
--- a/jstests/core/mr_merge.js
+++ b/jstests/core/mr_merge.js
@@ -1,3 +1,4 @@
+// Tests the 'merge' output mode for mapReduce.
 // Cannot implicitly shard accessed collections because of following errmsg: Cannot output to a
 // non-sharded collection because sharded collection exists already.
 // @tags: [
@@ -7,70 +8,97 @@
 //   does_not_support_stepdowns,
 //   uses_map_reduce_with_temp_collections,
 // ]
+(function() {
+"use strict";
+(function() {
+const source = db.mr_merge;
+source.drop();
 
-t = db.mr_merge;
-t.drop();
+assert.commandWorked(source.insert({_id: 1, a: [1, 2]}));
+assert.commandWorked(source.insert({_id: 2, a: [2, 3]}));
+assert.commandWorked(source.insert({_id: 3, a: [3, 4]}));
 
-t.insert({a: [1, 2]});
-t.insert({a: [2, 3]});
-t.insert({a: [3, 4]});
-
-outName = "mr_merge_out";
-out = db[outName];
+const out = db.mr_merge_out;
+const outName = out.getName();
 out.drop();
 
-m = function() {
-    for (i = 0; i < this.a.length; i++)
+const map = function() {
+    for (let i = 0; i < this.a.length; i++)
         emit(this.a[i], 1);
 };
-r = function(k, vs) {
+const reduce = function(k, vs) {
     return Array.sum(vs);
 };
 
-function tos(o) {
-    var s = "";
-    for (var i = 0; i < 100; i++) {
-        if (o[i])
-            s += i + "_" + o[i];
-    }
-    return s;
-}
-
-assert.commandWorked(t.mapReduce(m, r, {out: outName}));
-
-expected = {
-    "1": 1,
-    "2": 2,
-    "3": 2,
-    "4": 1
-};
-assert.eq(tos(expected), tos(out.convertToSingleObject("value")), "A");
+assert.commandWorked(source.mapReduce(map, reduce, {out: outName}));
+
+let expected = [{_id: 1, value: 1}, {_id: 2, value: 2}, {_id: 3, value: 2}, {_id: 4, value: 1}];
+assert.docEq(expected, out.find().sort({_id: 1}).toArray());
+
+assert.commandWorked(source.insert({_id: 4, a: [4, 5]}));
+// Insert something that should be unaltered by the mapReduce into the output collection.
+assert.commandWorked(out.insert({_id: 10, value: 5}));
+assert.commandWorked(
+    source.mapReduce(map, reduce, {out: {merge: outName}, query: {_id: {$gt: 3}}}));
+
+expected = [
+    {_id: 1, value: 1},
+    {_id: 2, value: 2},
+    {_id: 3, value: 2},
+    {_id: 4, value: 1},
+    {_id: 5, value: 1},
+    {_id: 10, value: 5}
+];
+assert.docEq(expected, out.find().sort({_id: 1}).toArray());
 
-t.insert({a: [4, 5]});
-out.insert({_id: 10, value: "5"});
-assert.commandWorked(t.mapReduce(m, r, {out: outName}));
+assert.commandWorked(source.insert({_id: 5, a: [5, 6]}));
+// Insert something that should be unaltered by the mapReduce into the output collection.
+assert.commandWorked(out.insert({_id: 20, value: 10}));
+assert.commandWorked(
+    source.mapReduce(map, reduce, {out: {merge: outName}, query: {_id: {$gt: 4}}}));
 
-expected["4"]++;
-expected["5"] = 1;
-assert.eq(tos(expected), tos(out.convertToSingleObject("value")), "B");
+expected = [
+    {_id: 1, value: 1},
+    {_id: 2, value: 2},
+    {_id: 3, value: 2},
+    {_id: 4, value: 1},
+    {_id: 5, value: 1},
+    {_id: 6, value: 1},
+    {_id: 10, value: 5},
+    {_id: 20, value: 10}
+];
+assert.docEq(expected, out.find().sort({_id: 1}).toArray());
+}());
+(function() {
+const source = db.mr_merge;
+source.drop();
 
-t.insert({a: [5, 6]});
-out.insert({_id: 10, value: "5"});
-assert.commandWorked(t.mapReduce(m, r, {out: {merge: outName}}));
+assert.commandWorked(source.insert({_id: 1, x: 1}));
+assert.commandWorked(source.insert({_id: 2, x: 1}));
+assert.commandWorked(source.insert({_id: 3, x: 2}));
 
-expected["5"]++;
-expected["10"] = 5;
-expected["6"] = 1;
+const out = db.mr_merge_out;
+const outName = out.getName();
+out.drop();
+
+const map = function() {
+    emit(this.x, 1);
+};
+const reduce = function(k, v) {
+    return Array.sum(v);
+};
 
-assert.eq(tos(expected), tos(out.convertToSingleObject("value")), "C");
+assert.commandWorked(
+    source.mapReduce(map, reduce, {out: {merge: outName}, query: {_id: {$gt: 0}}}));
 
-// test that the nonAtomic output gives valid result
-t.insert({a: [6, 7]});
-out.insert({_id: 20, value: "10"});
-assert.commandWorked(t.mapReduce(m, r, {out: {merge: outName, nonAtomic: true}}));
+assert.eq(2, out.findOne({_id: 1}).value);
+assert.eq(1, out.findOne({_id: 2}).value);
 
-expected["6"]++;
-expected["20"] = 10;
-expected["7"] = 1;
+assert.commandWorked(source.insert({_id: 4, x: 2}));
+assert.commandWorked(
+    source.mapReduce(map, reduce, {out: {merge: outName}, query: {_id: {$gt: 3}}}));
 
-assert.eq(tos(expected), tos(out.convertToSingleObject("value")), "D");
+assert.eq(2, out.findOne({_id: 1}).value);
+assert.eq(1, out.findOne({_id: 2}).value);
+}());
+}());
diff --git a/jstests/core/mr_merge2.js b/jstests/core/mr_merge2.js
deleted file mode 100644
index df2ada36749..00000000000
--- a/jstests/core/mr_merge2.js
+++ /dev/null
@@ -1,55 +0,0 @@
-// Cannot implicitly shard accessed collections because of following errmsg: Cannot output to a
-// non-sharded collection because sharded collection exists already.
-// @tags: [
-//   assumes_unsharded_collection,
-//   # mapReduce does not support afterClusterTime.
-//   does_not_support_causal_consistency,
-//   does_not_support_stepdowns,
-//   uses_map_reduce_with_temp_collections,
-// ]
-t = db.mr_merge2;
-t.drop();
-
-t.insert({a: [1, 2]});
-t.insert({a: [2, 3]});
-t.insert({a: [3, 4]});
-
-outName = "mr_merge2_out";
-out = db[outName];
-out.drop();
-
-m = function() {
-    for (i = 0; i < this.a.length; i++)
-        emit(this.a[i], 1);
-};
-r = function(k, vs) {
-    return Array.sum(vs);
-};
-
-function tos(o) {
-    var s = "";
-    for (var i = 0; i < 100; i++) {
-        if (o[i])
-            s += i + "_" + o[i] + "|";
-    }
-    return s;
-}
-
-outOptions = {
-    out: {merge: outName}
-};
-
-res = t.mapReduce(m, r, outOptions);
-expected = {
-    "1": 1,
-    "2": 2,
-    "3": 2,
-    "4": 1
-};
-assert.eq(tos(expected), tos(out.convertToSingleObject("value")), "A");
-
-t.insert({a: [4, 5]});
-res = t.mapReduce(m, r, outOptions);
-expected["4"]++;
-expected["5"] = 1;
-assert.eq(tos(expected), tos(out.convertToSingleObject("value")), "B");
diff --git a/jstests/core/mr_mutable_properties.js b/jstests/core/mr_mutable_properties.js
index d93ab8ce343..0110a7a858c 100644
--- a/jstests/core/mr_mutable_properties.js
+++ b/jstests/core/mr_mutable_properties.js
@@ -7,11 +7,13 @@
 // See SERVER-9448
 // Test argument and receiver (aka 'this') objects and their children can be mutated
 // in Map, Reduce and Finalize functions
-var collection = db.mrMutableReceiver;
+(function() {
+"use strict";
+const collection = db.mrMutableReceiver;
 collection.drop();
 collection.insert({a: 1});
 
-var map = function() {
+const map = function() {
     // set property on receiver
     this.feed = {beef: 1};
 
@@ -21,7 +23,7 @@ var map = function() {
     emit(this._id, this.a);
 };
 
-var reduce = function(key, values) {
+const reduce = function(key, values) {
     // set property on receiver
     this.feed = {beat: 1};
 
@@ -39,7 +41,7 @@ var reduce = function(key, values) {
     return {food: values};
 };
 
-var finalize = function(key, values) {
+const finalize = function(key, values) {
     // set property on receiver
     this.feed = {ice: 1};
 
@@ -58,7 +60,7 @@ var finalize = function(key, values) {
     return values;
 };
 
-var mr = collection.mapReduce(map, reduce, {finalize: finalize, out: {inline: 1}});
+const mr = collection.mapReduce(map, reduce, {finalize: finalize, out: {inline: 1}});
 printjson(mr);
 
 // verify mutated properties exist (order dictated by emit sequence and properties added)
@@ -71,3 +73,4 @@ assert.eq(mr.results[0].value.food[5].cream, 1);
 mr.results[0].value.food.forEach(function(val) {
     assert.eq(val.mod, 1);
 });
+}());
diff --git a/jstests/core/mr_outreduce.js b/jstests/core/mr_outreduce.js
deleted file mode 100644
index ff9e297a5d2..00000000000
--- a/jstests/core/mr_outreduce.js
+++ /dev/null
@@ -1,65 +0,0 @@
-// Cannot implicitly shard accessed collections because of following errmsg: Cannot output to a
-// non-sharded collection because sharded collection exists already.
-// @tags: [
-//   assumes_unsharded_collection,
-//   # mapReduce does not support afterClusterTime.
-//   does_not_support_causal_consistency,
-//   does_not_support_stepdowns,
-//   uses_map_reduce_with_temp_collections,
-// ]
-
-t = db.mr_outreduce;
-t.drop();
-
-t.insert({_id: 1, a: [1, 2]});
-t.insert({_id: 2, a: [2, 3]});
-t.insert({_id: 3, a: [3, 4]});
-
-outName = "mr_outreduce_out";
-out = db[outName];
-out.drop();
-
-m = function() {
-    for (i = 0; i < this.a.length; i++)
-        emit(this.a[i], 1);
-};
-r = function(k, vs) {
-    return Array.sum(vs);
-};
-
-function tos(o) {
-    var s = "";
-    for (var i = 0; i < 100; i++) {
-        if (o[i])
-            s += i + "_" + o[i] + "|";
-    }
-    return s;
-}
-
-assert.commandWorked(t.mapReduce(m, r, {out: outName}));
-
-expected = {
-    "1": 1,
-    "2": 2,
-    "3": 2,
-    "4": 1
-};
-assert.eq(tos(expected), tos(out.convertToSingleObject("value")), "A");
-
-t.insert({_id: 4, a: [4, 5]});
-out.insert({_id: 10, value: "5"});  // this is a sentinal to make sure it wasn't killed
-assert.commandWorked(t.mapReduce(m, r, {out: {reduce: outName}, query: {_id: {$gt: 3}}}));
-
-expected["4"]++;
-expected["5"] = 1;
-expected["10"] = 5;
-assert.eq(tos(expected), tos(out.convertToSingleObject("value")), "B");
-
-t.insert({_id: 5, a: [5, 6]});
-out.insert({_id: 20, value: "10"});  // this is a sentinal to make sure it wasn't killed
-assert.commandWorked(t.mapReduce(m, r, {out: {reduce: outName}, query: {_id: {$gt: 4}}}));
-
-expected["5"]++;
-expected["6"] = 1;
-expected["20"] = 10;
-assert.eq(tos(expected), tos(out.convertToSingleObject("value")), "C");
diff --git a/jstests/core/mr_outreduce2.js b/jstests/core/mr_outreduce2.js
deleted file mode 100644
index a309ad91af8..00000000000
--- a/jstests/core/mr_outreduce2.js
+++ /dev/null
@@ -1,39 +0,0 @@
-// Cannot implicitly shard accessed collections because of following errmsg: Cannot output to a
-// non-sharded collection because sharded collection exists already.
-// @tags: [
-//   assumes_unsharded_collection,
-//   # mapReduce does not support afterClusterTime.
-//   does_not_support_causal_consistency,
-//   does_not_support_stepdowns,
-//   uses_map_reduce_with_temp_collections,
-// ]
-
-normal = "mr_outreduce2";
-out = normal + "_out";
-
-t = db[normal];
-t.drop();
-
-db[out].drop();
-
-t.insert({_id: 1, x: 1});
-t.insert({_id: 2, x: 1});
-t.insert({_id: 3, x: 2});
-
-m = function() {
-    emit(this.x, 1);
-};
-r = function(k, v) {
-    return Array.sum(v);
-};
-
-res = t.mapReduce(m, r, {out: {reduce: out}, query: {_id: {$gt: 0}}});
-
-assert.eq(2, db[out].findOne({_id: 1}).value, "A1");
-assert.eq(1, db[out].findOne({_id: 2}).value, "A2");
-
-t.insert({_id: 4, x: 2});
-res = t.mapReduce(m, r, {out: {reduce: out}, query: {_id: {$gt: 3}}});
-
-assert.eq(2, db[out].findOne({_id: 1}).value, "B1");
-assert.eq(2, db[out].findOne({_id: 2}).value, "B2");
diff --git a/jstests/core/mr_reduce.js b/jstests/core/mr_reduce.js
new file mode 100644
index 00000000000..aded1cf471d
--- /dev/null
+++ b/jstests/core/mr_reduce.js
@@ -0,0 +1,104 @@
+// Tests the 'reduce' output mode for mapReduce.
+// Cannot implicitly shard accessed collections because of following errmsg: Cannot output to a
+// non-sharded collection because sharded collection exists already.
+// @tags: [
+//   assumes_unsharded_collection,
+//   # mapReduce does not support afterClusterTime.
+//   does_not_support_causal_consistency,
+//   does_not_support_stepdowns,
+//   uses_map_reduce_with_temp_collections,
+// ]
+(function() {
+"use strict";
+(function() {
+const source = db.mr_reduce;
+source.drop();
+
+assert.commandWorked(source.insert({_id: 1, a: [1, 2]}));
+assert.commandWorked(source.insert({_id: 2, a: [2, 3]}));
+assert.commandWorked(source.insert({_id: 3, a: [3, 4]}));
+
+const out = db.mr_reduce_out;
+const outName = out.getName();
+out.drop();
+
+const map = function() {
+    for (let i = 0; i < this.a.length; i++)
+        emit(this.a[i], 1);
+};
+const reduce = function(k, vs) {
+    return Array.sum(vs);
+};
+
+assert.commandWorked(source.mapReduce(map, reduce, {out: outName}));
+
+let expected = [{_id: 1, value: 1}, {_id: 2, value: 2}, {_id: 3, value: 2}, {_id: 4, value: 1}];
+assert.docEq(expected, out.find().sort({_id: 1}).toArray());
+
+assert.commandWorked(source.insert({_id: 4, a: [4, 5]}));
+// Insert something that should be unaltered by the mapReduce into the output collection.
+assert.commandWorked(out.insert({_id: 10, value: 5}));
+assert.commandWorked(
+    source.mapReduce(map, reduce, {out: {reduce: outName}, query: {_id: {$gt: 3}}}));
+
+expected = [
+    {_id: 1, value: 1},
+    {_id: 2, value: 2},
+    {_id: 3, value: 2},
+    {_id: 4, value: 2},
+    {_id: 5, value: 1},
+    {_id: 10, value: 5}
+];
+assert.docEq(expected, out.find().sort({_id: 1}).toArray());
+
+assert.commandWorked(source.insert({_id: 5, a: [5, 6]}));
+// Insert something that should be unaltered by the mapReduce into the output collection.
+assert.commandWorked(out.insert({_id: 20, value: 10}));
+assert.commandWorked(
+    source.mapReduce(map, reduce, {out: {reduce: outName}, query: {_id: {$gt: 4}}}));
+
+expected = [
+    {_id: 1, value: 1},
+    {_id: 2, value: 2},
+    {_id: 3, value: 2},
+    {_id: 4, value: 2},
+    {_id: 5, value: 2},
+    {_id: 6, value: 1},
+    {_id: 10, value: 5},
+    {_id: 20, value: 10}
+];
+assert.docEq(expected, out.find().sort({_id: 1}).toArray());
+}());
+(function() {
+const source = db.mr_reduce;
+source.drop();
+
+assert.commandWorked(source.insert({_id: 1, x: 1}));
+assert.commandWorked(source.insert({_id: 2, x: 1}));
+assert.commandWorked(source.insert({_id: 3, x: 2}));
+
+const out = db.mr_reduce_out;
+const outName = out.getName();
+out.drop();
+
+const map = function() {
+    emit(this.x, 1);
+};
+const reduce = function(k, v) {
+    return Array.sum(v);
+};
+
+assert.commandWorked(
+    source.mapReduce(map, reduce, {out: {reduce: outName}, query: {_id: {$gt: 0}}}));
+
+assert.eq(2, out.findOne({_id: 1}).value);
+assert.eq(1, out.findOne({_id: 2}).value);
+
+assert.commandWorked(source.insert({_id: 4, x: 2}));
+assert.commandWorked(
+    source.mapReduce(map, reduce, {out: {reduce: outName}, query: {_id: {$gt: 3}}}));
+
+assert.eq(2, out.findOne({_id: 1}).value);
+assert.eq(2, out.findOne({_id: 2}).value);
+}());
+}());
diff --git a/jstests/core/mr_undef.js b/jstests/core/mr_undef.js
deleted file mode 100644
index 5754a1c3084..00000000000
--- a/jstests/core/mr_undef.js
+++ /dev/null
@@ -1,33 +0,0 @@
-// @tags: [
-//   # mapReduce does not support afterClusterTime.
-//   does_not_support_causal_consistency,
-//   does_not_support_stepdowns,
-//   uses_map_reduce_with_temp_collections,
-// ]
-t = db.mr_undef;
-t.drop();
-
-outname = "mr_undef_out";
-out = db[outname];
-out.drop();
-
-t.insert({x: 0});
-
-var m = function() {
-    emit(this.mod, this.x);
-};
-var r = function(k, v) {
-    total = 0;
-    for (i in v) {
-        total += v[i];
-    }
-    return total;
-};
-
-res = t.mapReduce(m, r, {out: outname});
-
-assert.eq(0, out.find({_id: {$type: 6}}).itcount(), "A1");
-assert.eq(1, out.find({_id: {$type: 10}}).itcount(), "A2");
-
-x = out.findOne();
-assert.eq(x, out.findOne({_id: x["_id"]}), "A3");
diff --git a/jstests/perf/mr_bench.js b/jstests/perf/mr_bench.js
deleted file mode 100644
index c141e112163..00000000000
--- a/jstests/perf/mr_bench.js
+++ /dev/null
@@ -1,84 +0,0 @@
-
-t = db.mr_bench;
-t.drop();
-
-function getRandomStr(L) {
-    var s = '';
-    var randomchar = function() {
-        var n = Math.floor(Math.random() * 62);
-        if (n < 10)
-            return n;  // 1-10
-        if (n < 36)
-            return String.fromCharCode(n + 55);  // A-Z
-        return String.fromCharCode(n + 61);      // a-z
-    };
-    while (s.length < L)
-        s += randomchar();
-    return s;
-}
-
-t.ensureIndex({rand: 1}, {unique: true});
-
-largeStr = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
-while (largeStr.length < 512) {
-    largeStr += largeStr;
-}
-largeStr = largeStr.substr(512);
-
-for (i = 0; i < 100000; ++i) {
-    t.save({rand: getRandomStr(20), same: "the same string", str: largeStr});
-}
-
-emit = printjson;
-count = t.count();
-
-function d(x) {
-    printjson(x);
-}
-
-m = function() {
-    emit(this.rand, {id: this._id, str: this.str});
-};
-
-m2 = function() {
-    emit(this.same, this.rand);
-};
-
-r = function(k, vals) {
-    var tmp = {};
-    vals.forEach(function(i) {
-        if (typeof (i) == 'string') {
-            tmp[i] = true;
-        } else {
-            for (var z in i)
-                tmp[z] = true;
-        }
-    });
-
-    return tmp;
-};
-
-// following time limits are passing fine on a laptop with a debug build
-// so should always pass in theory unless something is wrong: GC, too much reducing, etc
-
-// 1st MR just uses random unique keys, with no reduce involved
-// this should be straightforward for perf, but could lead to OOM if settings are bad
-assert.time(function() {
-    res = db.runCommand({mapreduce: "mr_bench", map: m, reduce: r, out: "mr_bench_out"});
-    d(res);
-    assert.eq(count, res.counts.input, "A");
-    x = db[res.result];
-    assert.eq(count, x.find().count(), "B");
-    return 1;
-}, "unique key mr", 15000);
-
-// 2nd MR emits the same key, and a unique value is added as key to same object
-// if object is kept in ram and being reduced, this can be really slow
-assert.time(function() {
-    res = db.runCommand({mapreduce: "mr_bench", map: m2, reduce: r, out: "mr_bench_out"});
-    d(res);
-    assert.eq(count, res.counts.input, "A");
-    x = db[res.result];
-    assert.eq(1, x.find().count(), "B");
-    return 1;
-}, "single key mr", 20000);
diff --git a/jstests/perf/v8_mapreduce.js b/jstests/perf/v8_mapreduce.js
deleted file mode 100644
index 46afcf37082..00000000000
--- a/jstests/perf/v8_mapreduce.js
+++ /dev/null
@@ -1,118 +0,0 @@
-// Testing parallelism of mapReduce in V8
-
-// Our server and client need to be running V8 and the host we are running on needs at least two
-// cores.  Update this if you are testing more than three threads in parallel.
-if (/V8/.test(interpreterVersion()) && db.runCommand({buildinfo: 1}).javascriptEngine == "V8" &&
-    db.hostInfo().system.numCores >= 2) {
-    // function timeSingleThread
-    // Description: Gathers data about how long it takes to run a given job
-    // Args: job - job to run
-    //       tid - thread id passed as an argument to the job, default 0
-    // Returns: { threadStart : <time job started> , threadEnd : <time job completed> }
-    var timeSingleThread = function(job, tid) {
-        var tid = tid || 0;
-        var threadStart = new Date();
-        job(tid);
-        return {"threadStart": threadStart, "threadEnd": new Date()};
-    };
-
-    // function timeMultipleThreads
-    // Description: Gathers data about how long it takes to run a given job in multiple threads.
-    // Args: job - job to run in each thread
-    // nthreads - number of threads to spawn
-    // stagger - delay between each thread spawned in milliseconds
-    // Returns: Array with one entry for each thread of the form:
-    // [ { threadStart : <time elapsed before thread started work> ,
-    //     threadEnd : <time elapsed before thread completed work> } ,
-    //     ...
-    //     ]
-    var timeMultipleThreads = function(job, nthreads, stagger) {
-        var i = 0;
-        var threads = [];
-
-        for (i = 0; i < nthreads; ++i) {
-            threads[i] = new Thread(timeSingleThread, job, i);
-        }
-
-        // Our "reference time" that all threads agree on
-        var referenceTime = new Date();
-
-        for (i = 0; i < nthreads; ++i) {
-            if (stagger && i > 0) {
-                sleep(stagger);
-            }
-            threads[i].start();
-        }
-
-        var threadTimes = [];
-        for (i = 0; i < nthreads; ++i) {
-            var returnData = threads[i].returnData();
-            threadTimes[i] = {};
-            threadTimes[i].threadStart = returnData.threadStart - referenceTime;
-            threadTimes[i].threadEnd = returnData.threadEnd - referenceTime;
-        }
-
-        return threadTimes;
-    };
-
-    // Display and analysis helper functions
-
-    var getLastCompletion = function(threadTimes) {
-        var lastCompletion = 0;
-        for (var i = 0; i < threadTimes.length; i++) {
-            lastCompletion = Math.max(lastCompletion, threadTimes[i].threadEnd);
-        }
-        return lastCompletion;
-    };
-
-    // Functions we are performance testing
-
-    db.v8_parallel_mr_src.drop();
-
-    for (j = 0; j < 100; j++)
-        for (i = 0; i < 512; i++) {
-            db.v8_parallel_mr_src.save({j: j, i: i});
-        }
-
-    db.getLastError();
-
-    var mrWorkFunction = function() {
-        function verifyOutput(out) {
-            // printjson(out);
-            assert.eq(out.counts.input, 51200, "input count is wrong");
-            assert.eq(out.counts.emit, 51200, "emit count is wrong");
-            assert.gt(out.counts.reduce, 99, "reduce count is wrong");
-            assert.eq(out.counts.output, 512, "output count is wrong");
-        }
-
-        function map() {
-            if (this.j % 2 == 0) {
-                emit(this.i, this.j * this.j);
-            } else {
-                emit(this.i, this.j + this.j);
-            }
-        }
-
-        function reduce(key, values) {
-            values_halved = values.map(function(value) {
-                return value / 2;
-            });
-            values_halved_sum = Array.sum(values_halved);
-            return values_halved_sum;
-        }
-
-        var out = db.v8_parallel_mr_src.mapReduce(map, reduce, {out: "v8_parallel_mr_out"});
-        verifyOutput(out);
-    };
-
-    var oneMapReduce = getLastCompletion(timeMultipleThreads(mrWorkFunction, 1));
-    var twoMapReduce = getLastCompletion(timeMultipleThreads(mrWorkFunction, 2));
-    var threeMapReduce = getLastCompletion(timeMultipleThreads(mrWorkFunction, 3));
-
-    printjson("One map reduce job: " + oneMapReduce);
-    printjson("Two map reduce jobs: " + twoMapReduce);
-    printjson("Three map reduce jobs: " + threeMapReduce);
-
-    assert(oneMapReduce * 1.75 > twoMapReduce);
-    assert(oneMapReduce * 2.5 > threeMapReduce);
-}