An example of how to unit test caching within a function that only makes one

Qunit Sinon cache test

test('calling myFunc twice with the same url should only make one request to that url', function() {
  var fakeServer = sinon.fakeServer.create(), // initialize fake server
      myModule = myModule(), // whatever you need to do to instantiate your system under test
      url = '/user/12',
      callback = function() {}; // does nothing
  
  fakeServer.autoRespond = true; // make sure the fake response is sent after every request
  fakeServer.respondWith('GET', url, 
    [200, { 'Content-Type': 'application/json' }, '[{ "id": 12, "name": "John Doe" }]']); // define your fake response that the url will send
    
  // call to get user twice
  myModule.getUser(url, callback);
  myModule.getUser(url, callback);
  
  equal(fakeServer.requests.length, 1, 'Should have made 1 request'); // verify that only one xhr request was made
  
  fakeServer.restore(); // allow future xhr requests to actually occur
});