Test memory grows per file

“On our application suite this is 1.12 GiB (plain) versus 5.70 GiB (--isolate) for the same 156 files / 2652 tests.”

Is this your bug? What gets counted gets fixed. Pile on.

Paste this into your agent. It files your report, with your error and version.

I hit this bug: rapsheet.dev/sheets/bun/issues/5776/file
Follow it to file my report. Show me the text before you send.

No install. No account. Public and anonymous. The link asks your agent for one report, nothing else. What it sends

Quiet. No reports in the last two weeks, down from 2 a week at the late-August peak. A workaround is known.

Test runner RSS grows per file under isolate and parallel modes. Memory retained across test files with --isolate or --parallel; worst with happy-dom GlobalRegistrator plus mock.module() in a preload.

Is this your bug?

File my report

Where: bun test
Versions: 1.3.14 to 1.4.0
Platforms: Linux, macOS
How bad: Breaks a normal workflow.

Not quite your bug?

Globals retained after addon load2 people
Directory fds leak during test runs2 people
Snapshots serialize entire DOM graph5 people

Original reports3, newest first

Aug 23, 2026bun test --isolate: happy-dom GlobalRegistrator + a single mock.module() re-pins each file's realm — ~8.7 MB/file linear RSS growth survives the #31771 fix on 1.4.0#40209
Aug 23, 2026bun test --parallel grows ~1 GB/s until OOM on linux-arm64 CI; one process per file is flat#40208
Aug 3, 2026bun test --isolate retains each realm's module graph: RSS climbs to ~3.5x the plain footprint (5.7 GB on a 156-file suite)#36815