1 files changed, 65 insertions, 0 deletions
diff --git a/jstests/core/query/mr/mr_agg_explain.js b/jstests/core/query/mr/mr_agg_explain.js
new file mode 100644
index 00000000000..057b2fb8a3d
--- /dev/null
+++ b/jstests/core/query/mr/mr_agg_explain.js
@@ -0,0 +1,65 @@
+/**
+ * Tests that running mapReduce with explain behaves as expected.
+ * The test runs commands that are not allowed with security token: mapReduce.
+ * @tags: [
+ *   not_allowed_with_security_token,
+ *   incompatible_with_embedded,
+ *   # mapReduce does not support afterClusterTime.
+ *   does_not_support_causal_consistency,
+ * ]
+ */
+(function() {
+"use strict";
+
+load("jstests/libs/analyze_plan.js");  // For getPlanStages.
+
+const coll = db.mr_explain;
+coll.drop();
+assert.commandWorked(coll.createIndex({x: 1}));
+assert.commandWorked(coll.insert({x: 1}));
+
+function mapFunc() {
+    emit(this.x, 1);
+}
+
+function reduceFunc(key, values) {
+    return Array.sum(values);
+}
+
+function runTest(optionsObjOrOutString) {
+    // Succeeds for all modes when using agg map reduce.
+    for (let verbosity of ["queryPlanner", "executionStats", "allPlansExecution"]) {
+        const results =
+            coll.explain(verbosity).mapReduce(mapFunc, reduceFunc, optionsObjOrOutString);
+
+        // Check server info
+        assert(results.hasOwnProperty('serverInfo'), results);
+        assert.hasFields(results.serverInfo, ['host', 'port', 'version', 'gitVersion']);
+
+        const stages = getAggPlanStages(results, "$cursor");
+        assert(stages !== null);
+
+        // Verify that explain's output contains the fields that we expect.
+        // We loop through in the case that explain is run against a sharded cluster.
+        for (var i = 0; i < stages.length; i++) {
+            const stage = stages[i]["$cursor"];
+            if (verbosity != "allPlansExecution") {
+                assert(stage.hasOwnProperty(verbosity));
+            } else {
+                assert(stage.hasOwnProperty("executionStats"));
+                const execStats = stage["executionStats"];
+                assert(execStats.hasOwnProperty(verbosity));
+            }
+        }
+    }
+}
+
+// Test mapReduce explain with output to a collection.
+runTest("out_collection");
+
+// Test mapReduce explain with inline output.
+runTest({out: {inline: 1}});
+
+// Explain on mapReduce fails when the 3rd 'optionsOrOutString' argument is missing.
+assert.throws(() => coll.explain().mapReduce(mapFunc, reduceFunc));
+}());