tests/browser/server.py accepts --port 0: it binds 127.0.0.1:0 before
building the app, holds that socket for its whole life and prints
PM_TEST_SERVER_PORT=<n> to stdout. startBrowserServer defaults to port 0
and reads the announced port, so no port is reserved and released before
the server binds and two launchers can no longer race for one. The
"address already in use" retry and free-port.mjs are gone; --port N still
works and is checked against the announcement.
The page workflows started one global webServer and ran with one worker.
Each worker now owns its own tests/browser/server.py on an OS-chosen port,
with its own temp root and database, through a shared `test` in
tests/browser/fixtures.mjs. baseURL, and so page, request and
browser.newContext, point at that worker's server. A server that dies
fails the running test with its stderr tail and the next test gets a
fresh one. The worker count comes from PM_TEST_WORKERS, else 1 under CI,
else a quarter of the CPUs up to 8.
Chromium workflows in the pinned image: 510 tests in 606 s with one
worker on main, 511 (one new isolation spec) in 119 s with eight.
Vito Sansevero