hmr-test waits for compile signal (vercel#73064)

- The waitFor function now supports a predicate. Unlike retry, waitFor
does not include a timeout. Use it only when the predicate is guaranteed
to evaluate to true before proceeding to the next test. If it runs
indefinitely, Jest enforces a 120-second timeout per test.
- The getCliOutputFromHere utility provides a convenient string getter
that captures CLI output in between.

test/development/app-hmr/hmr.test.ts

@@ -62,7 +62,11 @@ describe(`app-dir-hmr`, () => {
       await browser.eval('window.__TEST_NO_RELOAD = true')
 
       expect(await browser.elementByCss('p').text()).toBe('mac')
+
+      const getCliOutput = next.getCliOutputFromHere()
       await next.patchFile(envFile, 'MY_DEVICE="ipad"', async () => {
+        await waitFor(() => getCliOutput().includes('Reload env'))
+
         await retry(async () => {
           expect(await browser.elementByCss('p').text()).toBe('ipad')
         })

test/integration/server-side-dev-errors/test/index.test.js

@@ -10,6 +10,7 @@ import {
   launchApp,
   retry,
   getRedboxSource,
+  assertNoRedbox,
 } from 'next-test-utils'
 import stripAnsi from 'strip-ansi'
 
@@ -93,7 +94,7 @@ describe('server-side dev errors', () => {
 
       expect(await getRedboxSource(browser)).toContain('missingVar')
       await fs.writeFile(gspPage, content, { flush: true })
-      await assertHasRedbox(browser)
+      await assertNoRedbox(browser)
     } finally {
       await fs.writeFile(gspPage, content)
     }
@@ -146,7 +147,7 @@ describe('server-side dev errors', () => {
 
       expect(await getRedboxSource(browser)).toContain('missingVar')
       await fs.writeFile(gsspPage, content)
-      await assertHasRedbox(browser)
+      await assertNoRedbox(browser)
     } finally {
       await fs.writeFile(gsspPage, content)
     }

test/lib/next-modes/base.ts

@@ -613,4 +613,11 @@ export class NextInstance {
       cb(...args)
     })
   }
+
+  public getCliOutputFromHere() {
+    const length = this.cliOutput.length
+    return () => {
+      return this.cliOutput.slice(length)
+    }
+  }
 }

test/lib/next-test-utils.ts

@@ -647,8 +647,21 @@ export async function stopApp(server: http.Server | undefined) {
   await promisify(server.close).apply(server)
 }
 
-export function waitFor(millis: number) {
-  return new Promise((resolve) => setTimeout(resolve, millis))
+export async function waitFor(
+  millisOrCondition: number | (() => boolean)
+): Promise<void> {
+  if (typeof millisOrCondition === 'number') {
+    return new Promise((resolve) => setTimeout(resolve, millisOrCondition))
+  }
+
+  return new Promise((resolve) => {
+    const interval = setInterval(() => {
+      if (millisOrCondition()) {
+        clearInterval(interval)
+        resolve()
+      }
+    }, 100)
+  })
 }
 
 export async function startStaticServer(