title: What is unit testing and how do you do it?
body: <h3>Exact duplicate of many posts:</h3>
  
  <p><a href="https://stackoverflow.com/questions/1383/what-is-unit-testing">What is unit testing?</a><br>
   <a href="https://stackoverflow.com/questions/61400/what-makes-a-good-unit-test">What Makes a Good Unit Test?</a><br>
   <a href="https://stackoverflow.com/questions/580960/new-to-unit-testing">New to Unit Testing</a><br>
   <a href="https://stackoverflow.com/questions/633053/unit-testing-definitions">Unit Testing - definitions</a><br>
   <a href="https://stackoverflow.com/questions/135651/learning-unit-testing">Learning Unit Testing</a><br>
   <a href="https://stackoverflow.com/questions/476540/how-to-properly-mock-and-unit-test">How to properly mock and unit test</a><br>
   <a href="https://stackoverflow.com/questions/473561/unit-testing-beginner-questions">Unit Testing: Beginner Questions</a><br>
   <a href="https://stackoverflow.com/questions/tagged/unit-testing">And many more ...</a><br>
   Also, Google for <a href="http://www.google.com/search?hl=en&amp;c2coff=1&amp;q=site%3Astackoverflow.com+%22how+do+you%22+unit-test&amp;btnG=Search" rel="noreferrer">site:stackoverflow.com "how do you" unit-test</a></p>
  
  <p>I have read some questions on unit testing, but I don't exactly know WHAT it is or how you do it. I was hoping if someone can tell me the following:</p>
  
  <ul>
  <li>What exactly IS unit testing? Is it built into code or run as separate programs? Or something else?</li>
  <li>How do you do it?</li>
  <li>When should it be done? Are there times or projects not to do it? Is everything unit-testable?</li>
  </ul>
  
  <p>Thanks a lot for the help.</p>