title: Jest/Frisby - FetchError: invalid json response body; how to log the server response
body: <p>I probably have an error on my server, because I get this from frisby:</p>
  
  <pre><code>FetchError: invalid json response body at ...
  </code></pre>
  
  <p>The problem is that I'm not able to see the server response, so I cannot understand what's going wrong.</p>
  
  <p>How can I log the server response using Frisby? I tried to log the response in the <em>then</em> function, without success:</p>
  
  <pre><code>frisby.use(spec =&gt; spec.setup({ request: { headers: { 'Token': token1 } } }))
      .post(BASE_URL + 'purchase', purchase)
      .expect('status', 409)  
      .then(res =&gt; {
        console.log(res);
      })
      .done(done);
  </code></pre>
  
  <p>Thanks</p>