Go E2E tests

An application in another process does not receive Go test state directly. It does inherit environment variables when started with exec.CommandContext and a nil Cmd.Env. Call fx.ShadowPG(t) before starting the process. The child then receives the fork’s DATABASE_URL and libpq PG* variables; application datasource code stays unchanged.

e2e_test.go

func TestBrowserCheckout(t *testing.T) {
  fx.ShadowPG(t)
  cmd := exec.CommandContext(t.Context(), "./app-test-server")
  // cmd.Env is nil, so os.Environ() is inherited at Start.
  if err := cmd.Start(); err != nil { t.Fatal(err) }
  t.Cleanup(func() {
    if cmd.Process != nil { _ = cmd.Process.Kill() }
    _ = cmd.Wait()
  })

  // Wait for the app's existing health endpoint, then drive its UI or API.
  waitForHealth(t, appURL)
  // browser.Navigate(appURL + "/checkout")
}

Import os/exec and testing. app-test-server, waitForHealth, and appURL represent your application’s existing launch and readiness conventions. Start one app per test or keep a worker’s app and fork alive, resetting that fork between sequential cases. Close database transactions before reset. Each concurrently running app should have its own fork and process.

ShadowPG changes the test process’s environment until test cleanup; Go forbids t.Parallel() in these tests. It cannot retarget a process that was already launched. If your launcher supplies an explicit Cmd.Env, copy os.Environ() after ShadowPG and add your app’s port and other settings to that slice.

Safe parallel execution

Use process-level workers: go test -p 4 ./... runs packages in separate test binaries, or launch disjoint go test -run ... -count=1 processes for one package. Each worker calls ShadowPG, starts its own app child after the environment is set, and uses a distinct HTTP port and browser session. Do not share one app process or fork across workers. Within a worker, finish browser requests, background database jobs, and transactions before resetting or closing its fork. t.Parallel() remains incompatible with ShadowPG, even if -parallel 1 is set.