[Bug]: Linearly-increased memory usage when using multiple jest.config.ts files + projects

[grxy]

Version

27.4.5

Steps to reproduce

1. Clone https://github.com/grxy/jest-memory-issue
2. Install dependencies with yarn
3. Run yarn jest-js and make note of the reported heap size
4. Run yarn jest-ts and notice that the heap size has increased
   It appears to increase linearly based on the number of jest.config.ts files being used.

Expected behavior

Memory usage should be consistent when using multiple jest.config.ts files + the projects config option.

Actual behavior

Memory usage increases when using multiple jest.config.ts files + the projects config option. Tests also execute more slowly.

Additional context

No response

Environment

System:
    OS: macOS 11.6
    CPU: (12) x64 Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
  Binaries:
    Node: 14.18.1 - ~/.nvm/versions/node/v14.18.1/bin/node
    Yarn: 1.22.17 - ~/.nvm/versions/node/v14.18.1/bin/yarn
    npm: 6.14.15 - ~/.nvm/versions/node/v14.18.1/bin/npm
  npmPackages:
    jest: ^27.4.5 => 27.4.5

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