Memory leak issue with jest

What is the expected behavior? Node heap size shouldn’t grow in every test.

What is the actual behavior? Heap size increases after every test file.

With nock:

PASS  test/function-86.js (22 MB heap size)
PASS  test/function-75.js (22 MB heap size)
PASS  test/function-1.js (22 MB heap size)
PASS  test/function-43.js (26 MB heap size)
PASS  test/function-24.js (26 MB heap size)
...
PASS  test/function-48.js (133 MB heap size)
PASS  test/function-82.js (137 MB heap size)
PASS  test/function-87.js (137 MB heap size)
PASS  test/function-20.js (137 MB heap size)
PASS  test/function-79.js (140 MB heap size)

Test Suites: 100 passed, 100 total
Tests:       100 passed, 100 total
Snapshots:   0 total
Time:        25.506s, estimated 26s

Without nock:

PASS  test/function-86.js (19 MB heap size)
PASS  test/function-75.js (19 MB heap size)
PASS  test/function-1.js (19 MB heap size)
PASS  test/function-65.js (19 MB heap size)
PASS  test/function-96.js (19 MB heap size)
...
PASS  test/function-93.js (20 MB heap size)
PASS  test/function-61.js (20 MB heap size)
PASS  test/function-49.js (20 MB heap size)
PASS  test/function-87.js (20 MB heap size)
PASS  test/function-79.js (20 MB heap size)

Test Suites: 100 passed, 100 total
Tests:       100 passed, 100 total
Snapshots:   0 total
Time:        27.079s

How to reproduce the issue

Even a single require/import of nock seems to cause the issue.

Minimal test case: https://github.com/juhosuominen/jest-nock-memory-leak

Versions

Software	Version(s)
Nock	11.7.0
Node	11.15.0

[RedTn]

This still seems to be an issue, though I can confirm that when I use node 11.15.0 and jest ^26 that there is no leak. As soon as I upgrade to node 16 (16.10.0) this is an issue again https://github.com/nock/nock/issues/2383

[mastermatt]

The discussion in Jest https://github.com/facebook/jest/issues/6814

And a nice write up on it. https://chanind.github.io/javascript/2019/10/12/jest-tests-memory-leak.html