Memory leak when just starting and stopping the server in jest test

Versions

• NodeJS: v14.18.1
• mongodb-memory-server-*: 8.9.5
• mongodb(the binary version): 0.0.0
• mongodb(the js package): 4.4.0
• system: MacOS

package: mongo-memory-server

What is the Problem?

Whenever I just start and stop the server I get a memory leak in my jest tests

Code Example

describe('testing, () => {
    let memorySever: MongoMemoryServer;

    beforeAll(async () => {
        memorySever = await MongoMemoryServer.create();
    });
    afterAll(async () => {
        await memorySever.stop();
        memorySever = undefined;
    });
    it("testing", async () => {

    });
});

Debug Output

Debug Output

  ● Test suite failed to run

    EXPERIMENTAL FEATURE!
    Your test suite is leaking memory. Please ensure all references are cleaned.

    There is a number of things that can leak memory:
      - Async operations that have not finished (e.g. fs.readFile).
      - Timers not properly mocked (e.g. setInterval, setTimeout).
      - Keeping references to the global scope.

      at onResult (../../node_modules/@jest/core/build/TestScheduler.js:190:18)
      at ../../node_modules/@jest/core/build/TestScheduler.js:316:17
      at ../../node_modules/emittery/index.js:260:13
          at Array.map (<anonymous>)
      at Emittery.emit (../../node_modules/emittery/index.js:258:23)

Do you know why it happenes?

no

[hasezoey]

i have investigated this a bit, and from what i can tell, it seems because for each jest test file / suite, jest will create a new context (including loading all modules), but does not remove that context after the suite (file) is finished, but keeps it until the end, which means jest will load modules (including MMS) over and over (which also includes the cached data, but cannot be accessed from the new contexts), i have also no clue if this is intentional in jest or how to disable it.

Disclaimer: i am not proficient in searching for memory leaks, and this was actually my first time using the memory inspector

So my recommendation is: stick to the integration guide (using global setup and global teardown), unless you are using only one suite / test file.

i will close this for now, because OP has found a fix

[hasezoey]

i suspect MMS means mongodb-memory-server ?

yes

if jest caches the context, including the loaded modules … this includes MMS … you are talking about some cache, what cache exactly and can one clear it?

like i said, i have no clue how to clear or disable it, it seems like jest just does not remove the suite contexts after use, because they are still referenced by the individual test results, or i might be completely wrong - like i said i am not proficient in debugging with the memory inspector (it was my first use of it)