test: allow generateWithPlugin & createTestProject to be invoked in the same file

Author: haoqunjiang

packages/@vue/cli-test-utils/createTestProject.js

@@ -3,6 +3,8 @@ const path = require('path')
 const execa = require('execa')
 
 module.exports = function createTestProject (name, preset, cwd, initGit) {
+  delete process.env.VUE_CLI_SKIP_WRITE
+
   cwd = cwd || path.resolve(__dirname, '../../test')
 
   const projectRoot = path.resolve(cwd, name)