test(flake): scoped per-test event-loop yield in the 6 dying spec files

JohnMcLear · claude · JohnMcLear · commit 1bf8a75c0cee · 2026-05-26T14:43:10.000+01:00
The Windows backend silent-ELIFECYCLE flake (12 captures so far across PRs #7838 / #7842 / #7846) clusters tightly to six spec files whose tests share a common shape: many short tests (50-100 in a single describe) firing rapid sequential supertest HTTP or socket.io connect/disconnect calls against the in-process Etherpad server. Pre-kill node-reports show the V8 main isolate becomes event-loop- starved 200-400 ms before each kill — the 5 Hz heartbeat falls silent for the entire death window — then the process is externally terminated bypassing every JS handler, --report-on-fatalerror, --report-uncaught-exception, signal handlers. PR #7852 ruled out TIME_WAIT accumulation as the proximate cause (the kill survived connection reuse, even though TIME_WAIT churn dropped to near zero). The actual trigger remains unidentified — but rapid sequential loopback I/O across test boundaries is the only common substrate across all six files. This patch adds a single setImmediate yield in beforeEach of each top-level describe in the six dying files. The yield forces the event loop to drain its timer queue between every test in those files, breaking the tight microtask chain that may be what triggers whatever native-level kill is happening on Windows + Node 24. Scope-critical: this is per-file beforeEach, NOT a root-level mochaHooks.beforeEach. The latter was tried in #7844 and broke ep_subscript_and_superscript's tests, which share state across describe-block boundaries and don't tolerate a yield. Per-file scope contains any timing perturbation to the affected files. Plugin tests loaded from `../node_modules/ep_*/static/tests/backend/specs` are completely untouched. Files modified (with death counts in parens): - src/tests/backend/specs/api/pad.ts (2) - src/tests/backend/specs/api/importexportGetPost.ts (4) - src/tests/backend/specs/socketio.ts (3) - src/tests/backend/specs/messages.ts (3) - src/tests/backend/specs/import.ts (1) - src/tests/backend/specs/clientvar_rev_consistency.ts (1) Test plan: - Linux ± plugins must pass. If they regress, the yield is breaking the affected tests' own state-sharing assumptions — we'd revert. - Windows ± plugins: pre-fix flake rate is ~22% per #7663 (13/60 runs). If the post-fix rate drops materially over 5-10 reruns, rapid-sequential-cadence is the trigger and this is a working mitigation. If unchanged, cadence is ruled out and we look at per-test pathologies (jose CNG on Windows, specific Express middleware paths, libuv IOCP edge cases unrelated to load). Either outcome is a strict improvement on the current state of "we have no idea what's causing it." Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
diff --git a/src/tests/backend/specs/api/importexportGetPost.ts b/src/tests/backend/specs/api/importexportGetPost.ts
@@ -37,6 +37,11 @@ const deleteTestPad = async () => {
 
 describe(__filename, function () {
   this.timeout(45000);
+  // Per-test setImmediate yield against the Windows backend silent-ELIFECYCLE
+  // flake. See rationale in api/pad.ts.
+  beforeEach(async function () {
+    await new Promise((r) => setImmediate(r));
+  });
   before(async function () { agent = await common.init(); });
 
   describe('Connectivity', function () {
diff --git a/src/tests/backend/specs/api/pad.ts b/src/tests/backend/specs/api/pad.ts
@@ -49,6 +49,19 @@ const ulSpaceHtml = '<!doctype html><html><body><ul class="bullet"> <li>one</li>
 const expectedSpaceHtml = '<!doctype html><html><body><ul class="bullet"><li>one</ul></body></html>';
 
 describe(__filename, function () {
+  // Per-test setImmediate yield. The Windows backend-test silent-ELIFECYCLE
+  // flake (12 captures so far, see PR #7838+#7842+#7846 diagnostics) shows
+  // event-loop starvation 200-400 ms before each kill, in tests that fire
+  // 50-100/s with rapid sequential loopback HTTP. This yield forces the
+  // event loop to service its timer queue between every test in this file,
+  // collapsing the back-to-back microtask chains that may be the trigger.
+  // Scoped per-file rather than at the root mocha hook level because
+  // PR #7844 demonstrated that a root-level yield breaks plugin tests
+  // that share state across describe-block boundaries.
+  beforeEach(async function () {
+    await new Promise((r) => setImmediate(r));
+  });
+
   before(async function () {
     agent = await common.init();
     const res = await agent.get('/api/')
diff --git a/src/tests/backend/specs/clientvar_rev_consistency.ts b/src/tests/backend/specs/clientvar_rev_consistency.ts
@@ -21,6 +21,11 @@ const settings = require('../../../node/utils/Settings');
 import {randomString} from '../../../static/js/pad_utils';
 
 describe(__filename, function () {
+  // Per-test setImmediate yield against the Windows backend silent-ELIFECYCLE
+  // flake. See rationale in api/pad.ts.
+  beforeEach(async function () {
+    await new Promise((r) => setImmediate(r));
+  });
   let agent: any;
   let clientVarsBackup: any;
   let loadTestBackup: boolean;
diff --git a/src/tests/backend/specs/import.ts b/src/tests/backend/specs/import.ts
@@ -11,6 +11,11 @@ const padManager = require('../../../node/db/PadManager');
 import settings from '../../../node/utils/Settings';
 
 describe(__filename, function () {
+  // Per-test setImmediate yield against the Windows backend silent-ELIFECYCLE
+  // flake. See rationale in api/pad.ts.
+  beforeEach(async function () {
+    await new Promise((r) => setImmediate(r));
+  });
   const settingsBackup: MapArrayType<any> = {};
   let agent: any;
 
diff --git a/src/tests/backend/specs/messages.ts b/src/tests/backend/specs/messages.ts
@@ -10,6 +10,11 @@ const plugins = require('../../../static/js/pluginfw/plugin_defs');
 import readOnlyManager from '../../../node/db/ReadOnlyManager';
 
 describe(__filename, function () {
+  // Per-test setImmediate yield against the Windows backend silent-ELIFECYCLE
+  // flake. See rationale in api/pad.ts.
+  beforeEach(async function () {
+    await new Promise((r) => setImmediate(r));
+  });
   let agent:any;
   let pad:PadType|null;
   let padId: string;
diff --git a/src/tests/backend/specs/socketio.ts b/src/tests/backend/specs/socketio.ts
@@ -12,6 +12,11 @@ const socketIoRouter = require('../../../node/handler/SocketIORouter');
 
 describe(__filename, function () {
   this.timeout(30000);
+  // Per-test setImmediate yield against the Windows backend silent-ELIFECYCLE
+  // flake. See rationale in api/pad.ts.
+  beforeEach(async function () {
+    await new Promise((r) => setImmediate(r));
+  });
   let agent: any;
   let authorize:Function;
   const backups:MapArrayType<any> = {};
