mongo/jstests/noPassthrough/query/match_expression_optimization_failpoint.js

// Tests that match expression optimization works properly when the failpoint isn't triggered, and
// is disabled properly when it is triggered.
Random.setRandomSeed();

const conn = MongoRunner.runMongod({});
assert.neq(conn, null, "Mongod failed to start up.");
const testDb = conn.getDB("test");
const coll = testDb.agg_opt;

const kTestZip = 44100;
for (let i = 0; i < 25; ++i) {
    assert.commandWorked(coll.insert({_id: kTestZip + i, city: "Cleveland", pop: Random.randInt(100000), state: "OH"}));
}

const pipeline = [{$match: {_id: {$in: [kTestZip]}}}, {$sort: {_id: 1}}];

const enabledPlan = coll.explain().aggregate(pipeline);
// Test that a single equality condition $in was optimized to an $eq.
assert.eq(enabledPlan.queryPlanner.parsedQuery._id.$eq, kTestZip);

const enabledResult = coll.aggregate(pipeline).toArray();

// Enable a failpoint that will cause match expression optimizations to be skipped.
assert.commandWorked(testDb.adminCommand({configureFailPoint: "disableMatchExpressionOptimization", mode: "alwaysOn"}));

const disabledPlan = coll.explain().aggregate(pipeline);
// Test that the $in query still exists and hasn't been optimized to an $eq.
assert.eq(disabledPlan.queryPlanner.parsedQuery._id.$in, [kTestZip]);

const disabledResult = coll.aggregate(pipeline).toArray();

// Test that the result is the same with and without optimizations enabled (result is sorted).
assert.eq(enabledResult, disabledResult);

MongoRunner.stopMongod(conn);