title: Why does my array update when method called live but doesn't in unit tests?
body: <p>I have a method called <code>toggleSelect</code> that adds and removes objects from an array called <code>selectedItems</code>. This works perfectly live in the browser.
  It doesn't seem to work during my unit test. Not clear why because I'm calling it directly from the component and passing it an argument. If I <code>console.log()</code> the item inside the method, it does display in the log correctly. The method runs, but the array never gets updated to verify that it works.</p>
  
  <pre><code>let items = [{
    "ID": "12345",
    "Name": "Real Person",
    "Description": "How a real person ought to be described",
    "Date": "2015-04-12T04:24:49-07:00",
    "Amount": 120.23
  }]
  
  const wrapper = shallowMount(DataTable, {
    propsData:  { items }
  })
  
  // toggle method directly on component
  wrapper.vm.toggleSelect(items[0])
  
  // verify that the array has been updated
  console.log(DataTable.data().selectedItems)
  </code></pre>
  
  <p>The log shows an empty array just in the test.</p>