title: What happens when you call a test using HttpCalloutMock?
body: <p>This is not a code/case specific question.</p>
  <p>I am new to Apex, and I'm trying to test methods that do Callouts to external APIs. I understand that in order to test this method, I have to create a class that implements HttpCalloutMock and use it in my test.</p>
  <p>However, I want to know: in the Test, when I call the actual method I'm testing, does a call go out to the API behind the scenes? Or is the data I'm putting in the mock the only data that gets passed around?</p>
  <p>(I'm asking because, if the latter, wouldn't that mean these tests are extremely counterproductive and unnecessary?)</p>