title: Invalid Chai property when calling calledOnce
body: <p>I'm having problems writing tests in JavaScript with Sinon and Chai.
  I'm trying to check if a function is called on a spy and get I get</p>
  <blockquote>
  <p>&quot;Error: Invalid Chai property: calledOnce&quot;</p>
  </blockquote>
  <p>I'm doing the same thing in another project with the same test dependencies without any problem.</p>
  <pre><code>var udpSocketStub = this.sandbox.spy(udpSocket, 'send');
  expect(udpSocketStub).calledOnce; // SHOULD FAIL
  
  
  &quot;dependencies&quot;: {
    &quot;body-parser&quot;: &quot;~1.17.1&quot;,
    &quot;bootstrap&quot;: &quot;^4.0.0-alpha.6&quot;,
    &quot;chai&quot;: &quot;^4.1.0&quot;,
    &quot;co-mocha&quot;: &quot;^1.2.0&quot;,
    &quot;cookie-parser&quot;: &quot;~1.4.3&quot;,
    &quot;debug&quot;: &quot;~2.6.3&quot;,
    &quot;express&quot;: &quot;~4.15.2&quot;,
    &quot;jquery&quot;: &quot;^3.2.1&quot;,
    &quot;mocha&quot;: &quot;^3.4.2&quot;,
    &quot;morgan&quot;: &quot;~1.8.1&quot;,
    &quot;node-compass&quot;: &quot;0.2.3&quot;,
    &quot;pug&quot;: &quot;^2.0.0-rc.1&quot;,
    &quot;serve-favicon&quot;: &quot;~2.4.2&quot;,
    &quot;sinon&quot;: &quot;^2.3.8&quot;,
    &quot;sinon-chai&quot;: &quot;^2.12.0&quot;
  }
  </code></pre>