/**
 * Tests for explaining an aggregation pipeline which uses the $sample stage.
 * @tags: [
 *   assumes_read_concern_local,
 * ]
 */
(function() {
"use strict";

load("jstests/libs/analyze_plan.js");

const coll = db.explain_sample;
coll.drop();

let docsToInsert = [];
for (let i = 0; i < 1000; ++i) {
    docsToInsert.push({_id: i});
}
assert.commandWorked(coll.insert(docsToInsert));

// Verify that explain reports execution stats for the MULTI_ITERATOR stage. This is designed to
// reproduce SERVER-35973.
const explain =
    assert.commandWorked(coll.explain("allPlansExecution").aggregate([{$sample: {size: 10}}]));
const multiIteratorStages = getAggPlanStages(explain, "MULTI_ITERATOR");
assert.gt(multiIteratorStages.length, 0, tojson(explain));
assert.gt(multiIteratorStages.reduce((acc, stage) => acc + stage.nReturned, 0),
          0,
          tojson(multiIteratorStages));
assert.gt(multiIteratorStages.reduce((acc, stage) => acc + stage.advanced, 0),
          0,
          tojson(multiIteratorStages));
assert.gt(multiIteratorStages.reduce((acc, stage) => acc + stage.works, 0),
          0,
          tojson(multiIteratorStages));
}());