Getting MockClient memory leak log

[mir1198yusuf]

After running a bunch of unit-tests through jest, I get this log in the console.

(node:66873) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 start listeners added to [MockClient]. Use emitter.setMaxListeners() to increase limit
(Use `node --trace-warnings ...` to show where the warning was created)
(node:66873) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 query listeners added to [MockClient]. Use emitter.setMaxListeners() to increase limit
(node:66873) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 query-error listeners added to [MockClient]. Use emitter.setMaxListeners() to increase limit
(node:66873) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 query-response listeners added to [MockClient]. Use emitter.setMaxListeners() to increase limit

I dont know if this is of any concern or it is just due to large number of parallel running async test functions.

Thanks.

[mir1198yusuf]

I have total 13 trackers.on in directory of unit-tests.

[felixmosh]

By trackers.on do you mean the tracker that the lib comes with or something else?

Can you share small code snippet ?

[mir1198yusuf]

This is how I use it. Since we dont have step in this lib like knex-mock, I try to make it work this way.

test('Name ', async () => {
        
        const response = [
                response of 1st query, response of 2nd query
        ];
        const trx = await knexObj.transaction();

        const a = new A();
        let step = 0;

        tracker.on
            .any(({ method, sql, bindings }: RawQuery) => {
                if (step === 0) {
                    expect(method).toEqual('select');
                    expect(sql).toMatchInlineSnapshot(....);
                    expect(bindings).toEqual([...]);
                }
                step++;

                return true;
            })
            .response(() => {
                return response[step - 1];
            });
        await a.b(trx)
        await trx.commit()
});

[mir1198yusuf]

By trackers.on do you mean the tracker that the lib comes with or something else?

Tracker of this lib.

[felixmosh]

Tracker.on is not using listeners at all

[felixmosh]

Your tests are not written as it meant to be used :]
You should no expect inside query matcher (the on part).
The lib provides an history object for each type of queries (select / insert ...)

test('Name ', async () => {
  const trx = await knexObj.transaction();

  const a = new A();
  tracker.on.select(({ sql }) => sql.includes('table_name')).responseOnce({ id: 1, name: 'bla' });
  await a.b(trx);
  await trx.commit();

  expect(tracker.history.select[0].sql).toContain('table_name');
});

Tracker is the one thing that you provide with the query response for a specific query type, and it contains the call history for each one of the requests.

[mir1198yusuf]

• I cannot just rely on sql.includes('table_name')) as all queries might be on same table.
• I want to match entire sql which I am doing using matchInlineSnapshot to see if new commit has not unintentionally added/removed query select/returning fields or where clauses or anything else. If it was an intentional change, I can update the jest snapshot of the sql.
• I cannot provide a complete sql to match with since it can be large & complex. So using snapshot of generated sql was the easy way for me. Jest automatically saves the generated sql as snapshot to compare next time test is run.
• I want to test the order of query in code. No one should unintentionally alter the sequence of queries. This I agree that I can it with tracker.history.any but since I have send response also to queries sequentially, I have to use step for response. (For first query hitting the client, this response should be send. For second, this should be send & so on). Since step is being used in response, I have to maintain (increment) it inside query matcher. So added expect there only, so it can fail early if a particular query is not as expected instead of knowing this at end using tracker.history.any. (Should-be second query is unintentionally changed to first query)

[mir1198yusuf]

Tracker.on is not using listeners at all

Okay! The logs in the first comment regarding listeners in MockClient do not hint any serious concerns right ? In this case, we can close the issue.

[mir1198yusuf]

I ran node --trace-warnings node_modules/jest/bin/jest.js to trace the log, I got this.

(node:71047) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 start listeners added to [MockClient]. Use emitter.setMaxListeners() to increase limit
    at _addListener (node:events:595:17)
    at MockClient.addListener (node:events:617:10)
    at makeTxClient (abc-user/node_modules/knex/lib/execution/transaction.js:335:13)
    at abc-user/node_modules/knex/lib/execution/transaction.js:196:43
    at Transaction_PG.acquireConnection (abc-user/node_modules/knex/lib/execution/transaction.js:254:20)
(node:71047) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 query listeners added to [MockClient]. Use emitter.setMaxListeners() to increase limit
    at _addListener (node:events:595:17)
    at MockClient.addListener (node:events:617:10)
    at makeTxClient (abc-user/node_modules/knex/lib/execution/transaction.js:340:13)
    at abc-user/node_modules/knex/lib/execution/transaction.js:196:43
    at Transaction_PG.acquireConnection (abc-user/node_modules/knex/lib/execution/transaction.js:254:20)
(node:71047) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 query-error listeners added to [MockClient]. Use emitter.setMaxListeners() to increase limit
    at _addListener (node:events:595:17)
    at MockClient.addListener (node:events:617:10)
    at makeTxClient (abc-user/node_modules/knex/lib/execution/transaction.js:345:13)
    at abc-user/node_modules/knex/lib/execution/transaction.js:196:43
    at Transaction_PG.acquireConnection (abc-user/node_modules/knex/lib/execution/transaction.js:254:20)
(node:71047) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 query-response listeners added to [MockClient]. Use emitter.setMaxListeners() to increase limit
    at _addListener (node:events:595:17)
    at MockClient.addListener (node:events:617:10)
    at makeTxClient (abc-user/node_modules/knex/lib/execution/transaction.js:350:13)
    at abc-user/node_modules/knex/lib/execution/transaction.js:196:43
    at Transaction_PG.acquireConnection (abc-user/node_modules/knex/lib/execution/transaction.js:254:20)

The warnings are created from knex lib, not this lib.

Found several issues for this on knex repo, will check in detail soon. Can close this issue