Slow performances when running tests with `--experimental-test-coverage`

Version

v22.9.0

Platform

Darwin N4V4PGFGPT 23.6.0 Darwin Kernel Version 23.6.0: Mon Jul 29 21:16:46 PDT 2024; root:xnu-10063.141.2~1/RELEASE_ARM64_T8112 arm64

Subsystem

No response

What steps will reproduce the bug?

Run tests with --experimental-test-coverage option. Comparing it to other solutions (f.e. running Node tests and getting the coverage with nyc) this is way slower. For instance, on a repo with ~800 tests, collecting coverage with nyc takes 77s, while running with --experimental-test-coverage takes 148s.

How often does it reproduce? Is there a required condition?

I can reproduce it every time I run the Node tests with the native test coverage option.

What is the expected behavior? Why is that the expected behavior?

The performances should be at least equal (ideally better) than with 3rd party dependencies (like nyc).

What do you see instead?

An average time spent per test of 185ms vs 96ms.

Additional information

I tried running with/without additional options (f.e. --test-coverage-exclude, --test-coverage-include, --test-coverage-branches, --test-coverage-functions, --test-coverage-lines) but it didn't help. The performance issue seems only to be related to the algorithm that's triggered by the --experimental-test-coverage option.

Start by reproducing the reported timings with a test suite of roughly 800 tests, comparing --experimental-test-coverage with nyc and the listed coverage options. Trace the coverage algorithm triggered by the native option; done means coverage remains correct while its performance is substantially closer to the comparison.