test: wait for logs to appear in end-to-end test

This test has been very flaky, I think this is because Pino uses async
logs and sometimes the log doesn't appear immediately. This should
address the race condition where our tests run before the log has had
time to come through.

Author: rowanmanning

packages/middleware-log-errors/test/end-to-end/index.spec.js

@@ -1,4 +1,5 @@
 const { fork } = require('node:child_process');
+const { setTimeout } = require('node:timers/promises');
 
 describe('@dotcom-reliability-kit/middleware-log-errors end-to-end', () => {
 	let child;
@@ -28,6 +29,19 @@ describe('@dotcom-reliability-kit/middleware-log-errors end-to-end', () => {
 	describe('GET /error', () => {
 		beforeAll(async () => {
 			await fetch(`${baseUrl}/error`);
+
+			// Pino uses async logs so we can't guarantee that our log will have been output
+			// immediately. We wait a total of 5s for the log to come through, checking for
+			// the log in 100ms increments
+			let waitTime = 0;
+			while (waitTime < 5000) {
+				if (stdout.includes('HANDLED_ERROR')) {
+					return;
+				}
+				waitTime += 100;
+				await setTimeout(100);
+			}
+			throw new Error('HANDLED_ERROR log took too long to come through');
 		});
 
 		it('logs error information to stdout', () => {