build: ensure runner is defined inside the spec callback (#17664)

spec-main/index.js

@@ -75,6 +75,8 @@ app.whenReady().then(() => {
 
   walker.on('end', () => {
     const runner = mocha.run(() => {
+      // Ensure the callback is called after runner is defined
+      process.nextTick(() => {
         if (isCi && runner.hasOnly) {
           try {
             throw new Error('A spec contains a call to it.only or describe.only and should be reverted.')
@@ -87,4 +89,5 @@ app.whenReady().then(() => {
         process.exit(runner.failures)
       })
     })
+  })
 })

spec/static/index.html

@@ -94,6 +94,8 @@
     }
 
     const runner = mocha.run(() => {
+      // Ensure the callback is called after runner is defined
+      setTimeout(() => {
         if (isCi && runner.hasOnly) {
           try {
             throw new Error('A spec contains a call to it.only or describe.only and should be reverted.')
@@ -109,6 +111,7 @@
         if (isCi) {
           ipcRenderer.send('process.exit', runner.failures)
         }
+      }, 0)
     })
   })
 })()