Stop printing webpack assets while testing

How can I stop printing webpack assets while testing in nuxtjs? I am using ava. I tried to set webpack stats in nuxt.config but it is not working:

// Does not work
{
  ...
  build: {
    ...
    extend (config, { isClient }) {
      ...
      if (process.env.NODE_ENV === 'test') {
        config.stats = 'errors-only'
      }
    }
  }
 ...
}

What am I trying to do is to stop showing logs like this from Webpack:

Hash: 5a2a3d23f88174970ed8
Version: webpack 3.12.0
Time: 22209ms
                                         Asset       Size  Chunks                    Chunk Names
   pages/widgets/index.51838abe9967a9e0b5ff.js    1.17 kB      10  [emitted]         pages/widgets/index
                       img/icomoon.7f1da5a.svg    5.38 kB          [emitted]         
                     fonts/icomoon.2d429d6.ttf    2.41 kB          [emitted]         
           img/fontawesome-webfont.912ec66.svg     444 kB          [emitted]  [big]  
         fonts/fontawesome-webfont.b06871f.ttf     166 kB          [emitted]         
                        img/mobile.8891a7c.png    39.6 kB          [emitted]         
                   img/play_button.6b15900.png    14.8 kB          [emitted]         
                  img/keyword-back.f95e10a.jpg    43.4 kB          [emitted]         
                    fonts/icomoon.16db67c.woff    2.49 kB          [emitted]         
                     fonts/icomoon.2fcbf50.eot    2.58 kB          [emitted]         
         fonts/fontawesome-webfont.674f50d.eot     166 kB          [emitted]         
        fonts/fontawesome-webfont.fee66e7.woff      98 kB          [emitted]