code: function writeAppFile(filePath, content) {
    return new Promise((resolve, reject) => {
      const resolvedFilePath = path.join(path.resolve(tmp), 'src', 'app', filePath);
      fs.writeFile(resolvedFilePath, content, (err) => {
        if (err) {
          reject(err);
          return;
        }
  
        resolve();
      });
    });
  }
docs: Write a file into the src/app folder -- Used for injecting files prior to build
  that we don't want to include in the skyux-template but need to test