refactor(api-proxy): extract duplicate collectLogOutput() into shared test helper (#4207)

* Initial plan

* refactor: extract collectLogOutput into shared log-test-helpers.js

Resolves duplicate helper copied across three api-proxy test files.
Extract to containers/api-proxy/test-helpers/log-test-helpers.js and
import from there in the three consumers.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Author: Copilot

containers/api-proxy/guards/effective-token-guard.test.js

@@ -4,19 +4,7 @@ const {
   getEffectiveTokenReflectState,
   resetEffectiveTokenGuardForTests,
 } = require('./effective-token-guard');
-
-function collectLogOutput() {
-  const lines = [];
-  const spy = jest.spyOn(process.stdout, 'write').mockImplementation((data) => {
-    try {
-      lines.push(JSON.parse(data.toString()));
-    } catch {
-      // ignore non-JSON writes
-    }
-    return true;
-  });
-  return { lines, spy };
-}
+const { collectLogOutput } = require('../test-helpers/log-test-helpers');
 
 describe('effective-token-guard reflect state', () => {
   beforeEach(() => {

containers/api-proxy/server.billing.test.js

@@ -8,6 +8,7 @@ const https = require('https');
 const { EventEmitter } = require('events');
 
 const { validateApiKeys, keyValidationResults, resetKeyValidationState, extractBillingHeaders } = require('./server');
+const { collectLogOutput } = require('./test-helpers/log-test-helpers');
 
 // ── Helpers for validateApiKeys tests ──────────────────────────────────────────
 
@@ -32,22 +33,6 @@ function mockHttpsRequestWithStatus(statusCode) {
   });
 }
 
-/**
- * Collect structured log lines emitted by logRequest() (written to process.stdout).
- */
-function collectLogOutput() {
-  const lines = [];
-  const spy = jest.spyOn(process.stdout, 'write').mockImplementation((data) => {
-    try {
-      lines.push(JSON.parse(data.toString()));
-    } catch {
-      // ignore non-JSON writes
-    }
-    return true;
-  });
-  return { lines, spy };
-}
-
 function createValidationAdapter(name, probe) {
   return {
     name,

containers/api-proxy/server.lifecycle.test.js

@@ -10,19 +10,7 @@ const { EventEmitter } = require('events');
 
 const { fetchStartupModels, healthResponse, createProviderServer, resetModelCacheState } = require('./server');
 const { createCopilotAdapter } = require('./providers/copilot');
-
-function collectLogOutput() {
-  const lines = [];
-  const spy = jest.spyOn(process.stdout, 'write').mockImplementation((data) => {
-    try {
-      lines.push(JSON.parse(data.toString()));
-    } catch {
-      // ignore non-JSON writes
-    }
-    return true;
-  });
-  return { lines, spy };
-}
+const { collectLogOutput } = require('./test-helpers/log-test-helpers');
 
 describe('healthResponse', () => {
   afterEach(() => {

containers/api-proxy/test-helpers/log-test-helpers.js

@@ -0,0 +1,23 @@
+'use strict';
+
+/**
+ * Spy on process.stdout.write and collect any structured JSON log lines emitted
+ * during a test.  Call spy.mockRestore() (or jest.restoreAllMocks()) in afterEach
+ * to clean up.
+ *
+ * @returns {{ lines: object[], spy: jest.SpyInstance }}
+ */
+function collectLogOutput() {
+  const lines = [];
+  const spy = jest.spyOn(process.stdout, 'write').mockImplementation((data) => {
+    try {
+      lines.push(JSON.parse(data.toString()));
+    } catch {
+      // ignore non-JSON writes
+    }
+    return true;
+  });
+  return { lines, spy };
+}
+
+module.exports = { collectLogOutput };