The purpose of this repo is to provide a reproducible example for #7874.

How to run

I ran these tests with the following env:

npx envinfo --preset jest

  System:
    OS: macOS 10.15.5
    CPU: (8) x64 Intel(R) Core(TM) i7-8569U CPU @ 2.80GHz
  Binaries:
    Node: 14.3.0 - /usr/local/bin/node
    Yarn: 1.22.4 - ~/.yarn/bin/yarn
    npm: 6.13.7 - ~/.npm-global/bin/npm
  npmPackages:
    jest: ^26.0.1 => 26.0.1

To reproduce this issue, clone this repo and run locally or through Docker:

Local

yarn test

Docker

yarn docker test

 PASS  tests/simple23.test.js (300 MB heap size)
 PASS  tests/simple0.test.js (316 MB heap size)
 PASS  tests/simple4.test.js (316 MB heap size)
 PASS  tests/simple10.test.js (333 MB heap size)
 PASS  tests/simple26.test.js (333 MB heap size)
 PASS  tests/simple42.test.js (333 MB heap size)
 PASS  tests/simple15.test.js (348 MB heap size)

Test Suites: 50 passed, 50 total
Tests:       50 passed, 50 total
Snapshots:   0 total
Time:        7.191 s
Ran all test suites.
✨  Done in 8.29s.

---

Exposing Node's gc API via the --expose-gc flag seems to fix the problem (see package.json for exact script):

Local

yarn test-expose

Docker

yarn docker test-expose

 PASS  tests/simple35.test.js (36 MB heap size)
 PASS  tests/simple29.test.js (36 MB heap size)
 PASS  tests/simple3.test.js (36 MB heap size)
 PASS  tests/simple1.test.js (36 MB heap size)
 PASS  tests/simple34.test.js (36 MB heap size)
 PASS  tests/simple41.test.js (36 MB heap size)
 PASS  tests/simple32.test.js (36 MB heap size)

Test Suites: 50 passed, 50 total
Tests:       50 passed, 50 total
Snapshots:   0 total
Time:        8.144 s
Ran all test suites.
✨  Done in 8.82s.