title: Jest tests failing only with coverage
body: <p>I have the issue that if I run my test without the <code>--coverage</code> option everything passes, but as soon as I run <code>jest</code> with the <code>--coverage</code> option some of my test fail. </p>
  
  <p>Here is the log:</p>
  
  <pre><code>Button › Primary button › should render a primary button
  
    undefined:3:457: property missing ':'
  
    at Object.it (src/components/Buttons/Button/Button.test.js:13:24)
    at Promise.resolve.then.el (node_modules/p-map/index.js:46:16)
  </code></pre>
  
  <p>And the test:</p>
  
  <pre><code>it('should render a primary button', () =&gt; {
    const props = { primary: true };
  
    const rendered = renderer.create(&lt;Button { ...props }&gt;Some Button&lt;/Button&gt;).toJSON();
    expect(rendered).toMatchSnapshot();
  });
  </code></pre>
  
  <p>The failing line is <code>expect(rendered).toMatchSnapshot();</code></p>
  
  <p>Anyone any ideas?</p>