Memory Leak with just expect('a').toBe('a') 23 times in a file

[Garethp]

🐛 Bug Report

Jest appears to be leaking memory for no discernible reason. Just having expect('a').toBe('a') 23 times in a file with nothing else in the repository is enough to cause a leak

To Reproduce

Steps to reproduce the behavior:

• Have a file with 23 instances of expect('a').toBe('a')
• Copy that file 10 times
• Run those tests with --expose-gc, --runInBand and --logHeapUsage

Expected behavior

Memory should stay consistent and not leak.

Link to repl or repo (highly encouraged)

There's a repository to help reproduce it here

envinfo

  System:
    OS: Linux 5.4 Ubuntu 20.04.1 LTS (Focal Fossa)
    CPU: (4) x64 Intel(R) Core(TM) i7-7500U CPU @ 2.70GHz
  Binaries:
    Node: 12.16.1 - ~/.nvm/versions/node/v12.16.1/bin/node
    Yarn: 1.22.4 - ~/.nvm/versions/node/v12.16.1/bin/yarn
    npm: 6.13.4 - ~/.nvm/versions/node/v12.16.1/bin/npm
  npmPackages:
    jest: ^26.4.2 => 26.4.2 

[jaredjj3]

I have made a similar sample repo that produced similar results (see #7874): jest-memory-leak-demo.

[SimenB]

Forcing GC like mentioned in #7874 (comment) stabilizes the memory usage.

Very odd 22 vs 23 expects changes anything, but I'm guessing it triggers some heuristic within v8 that triggers some extra caching

[github-actions]

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