mongo/jstests/core/query/explain/explain_delete.js

/**
 * Tests for explaining the delete command.
 *
 * @tags: [
 *  no_selinux,
 *  requires_fastcount,
 *  requires_fcv_61,
 *  requires_non_retryable_writes,
 *  # Pre-images requires doc-by-doc deletion and this test relies on BATCHED_DELETE
 *  incompatible_with_preimages_by_default,
 *  ]
 */
import {checkNWouldDelete} from "jstests/libs/query/analyze_plan.js";

let collName = "jstests_explain_delete";
let t = db[collName];
t.drop();

let explain;

// Explain delete against an empty collection.
assert.commandWorked(db.createCollection(t.getName()));
explain = db.runCommand({explain: {delete: collName, deletes: [{q: {a: 1}, limit: 0}]}});
checkNWouldDelete(explain, 0);

// Add an index but no data, and check that the explain still works.
t.createIndex({a: 1});
explain = db.runCommand({explain: {delete: collName, deletes: [{q: {a: 1}, limit: 0}]}});
checkNWouldDelete(explain, 0);

// Add some copies of the same document.
for (let i = 0; i < 10; i++) {
    t.insert({a: 1});
}
assert.eq(10, t.count());

// Run an explain which shows that all 10 documents *would* be deleted.
explain = db.runCommand({explain: {delete: collName, deletes: [{q: {a: 1}, limit: 0}]}});
checkNWouldDelete(explain, 10);

// Make sure all 10 documents are still there.
assert.eq(10, t.count());

// If we run the same thing without the explain, then all 10 docs should be deleted.
let deleteResult = db.runCommand({delete: collName, deletes: [{q: {a: 1}, limit: 0}]});
assert.commandWorked(deleteResult);
assert.eq(0, t.count());