title: Sinon restore cannot read property 'restore' of undefined
body: <p>I have the following code which I am using Sinon for </p>
  
  <pre><code>import React from 'react';
  import { mount } from 'enzyme';
  import sinon from 'sinon';
  import { IncrementalSearch } from './IncrementalSearch';
  
  describe('&lt;IncrementalSearch /&gt;', () =&gt; {
  afterEach(() =&gt; {
     this.constructorSpy.restore();
  });
  
  it('calls constructor', () =&gt; {
      this.constructorSpy = sinon.spy(IncrementalSearch, 'constructor');
      const wrapper = mount(&lt;IncrementalSearch /&gt;);
      expect(IncrementalSearch.prototype.constructor.calledOnce).toEqual(true);
      // expect(1).toEqual(1);
  });
  </code></pre>
  
  <p>});</p>
  
  <p>Now when I run this I get the following error </p>
  
  <pre><code>  TypeError: Cannot read property 'restore' of undefined
  </code></pre>
  
  <p>What am I doing wrong here?</p>