title: Jest: react-router tests returns undefined 'params'
body: <p>I'm trying to test a component with the <code>MemoryRouter</code> as indicated in the React-router docs with initial entries set so I can have params inside the wrapped component.</p>
  
  <p>Component example :</p>
  
  <pre><code>render () {
    console.log(this.props.match.params.item)
  }
  </code></pre>
  
  <p>In the App (works fine) :</p>
  
  <pre><code>&lt;Router&gt;
    &lt;Switch&gt;
      &lt;Route exact path='/' render={() =&gt; (
        &lt;Redirect to={`/${guessLocale()}`} /&gt;
      )} /&gt;
      &lt;Route exact path='/:lang' component={Home} /&gt;
      &lt;Route exact path='/:lang/:itemName' component={Vidactic} /&gt;
    &lt;/Switch&gt;
  &lt;/Router&gt;
  </code></pre>
  
  <p>In the test (mount from Enzyme, match is undefined) :</p>
  
  <pre><code>mount(&lt;MemoryRouter initialEntries={['/fr/pamp']}&gt;
    &lt;Vidactic /&gt;
  &lt;/MemoryRouter&gt;)
  </code></pre>
  
  <p>So I used this workaround but why initialEntries would not work by itself ?</p>
  
  <pre><code>mount(&lt;MemoryRouter initialEntries={['/fr/pamp']}&gt;
    &lt;Vidactic match={{ params: { item: 'pamp' } }} /&gt;
  &lt;/MemoryRouter&gt;)
  </code></pre>