Memory Leak on using Jest Circus as the Test-Runner

[sauravhiremath]

Where did the memory leak originate?

How to reproduce the issue?

// Checkout PR 18
git fetch origin pull/18/head:individual-test-report

// Clean your yarn builds and re-build again
yarn clean-all
yarn

//Run this to reproduce the issue
JEST_CIRCUS=1 yarn test-leak

How does the "memory leak test fail" look?

    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 (packages/jest-core/build/TestScheduler.js:190:18)
          at Array.map (<anonymous>)

[kunal-kushwaha]

Reference: #6

[SimenB]

I won't have time to look into this properly until the weekend/next week, but jest-circus has always failed the test-leak script up until jestjs#9934 landed a couple of months ago. So I'd try to make sure you're rebased on top of master, and then try to do a bisect of all the commits on top of that.

[sauravhiremath]

This is a rough draft of how I traced the mem-leak. Will edit it later for a cleaner one

TestCaseReporterHandler.ts [sendMessageToJest(‘test-case-result’, testCaseResult)] -> TestRunner -> EventEmiiter.on(‘test-case-result’, (testCaseResult)) ->TestScheduler (onTestCaseResult) -> ReporterDispatcher (onTestCaseResult) -> default_reporter (onTestCaseResult) -> Status (addTestCaseResult())

Here, TestCaseReporterHandler emits test-case-result, but here it passes down the array reference and not a copy of array. Hence in all the flow mentioned above, the reference still persists causing testCaseResult to be present globally for all workers spawned.

This was avoided down the lane, in Status function by making a deepCyclicCopy of the array passed. Hence removing the global reference of the array once and for all, that too for all spawned workers

[github-actions]

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