spec: Add test case for app.relaunch

spec/fixtures/api/relaunch/main.js

@@ -0,0 +1,25 @@
+const {app, dialog} = require('electron')
+const net = require('net')
+
+const socketPath = process.platform === 'win32' ?
+  '\\\\.\\pipe\\electron-app-relaunch' :
+  '/tmp/electron-app-relaunch'
+
+process.on('uncaughtException', () => {
+  app.exit(1)
+})
+
+app.once('ready', () => {
+  let lastArg = process.argv[process.argv.length - 1]
+  const client = net.connect(socketPath)
+  client.once('connect', () => {
+    client.end(String(lastArg === '--second'))
+  })
+  client.once('end', () => {
+    app.exit(0)
+  })
+
+  if (lastArg !== '--second') {
+    app.relaunch({args: process.argv.slice(1).concat('--second')})
+  }
+})