Add spec for unhandledRejection event in main process

spec/static/main.js

@@ -275,16 +275,32 @@ ipcMain.on('try-emit-web-contents-event', (event, id, eventName) => {
 })
 
 ipcMain.on('handle-uncaught-exception', (event, message) => {
-  const listeners = process.listeners('uncaughtException')
-  process.removeAllListeners('uncaughtException')
-  process.on('uncaughtException', (error) => {
-    process.removeAllListeners('uncaughtException')
-    listeners.forEach((listener) => {
-      process.on('uncaughtException', listener)
-    })
+  suspendListeners(process, 'uncaughtException', (error) => {
     event.returnValue = error.message
   })
   fs.readFile(__filename, () => {
     throw new Error(message)
   })
 })
+
+ipcMain.on('handle-unhandled-rejection', (event, message) => {
+  suspendListeners(process, 'unhandledRejection', (error) => {
+    event.returnValue = error.message
+  })
+  fs.readFile(__filename, () => {
+    Promise.reject(new Error(message))
+  })
+})
+
+// Suspend listeners until the next event and then restore them
+const suspendListeners = (emitter, eventName, callback) => {
+  const listeners = emitter.listeners(eventName)
+  emitter.removeAllListeners(eventName)
+  emitter.once(eventName, (...args) => {
+    emitter.removeAllListeners(eventName)
+    listeners.forEach((listener) => {
+      emitter.on(eventName, listener)
+    })
+    callback(...args)
+  })
+}