title: What would you do when you are about to add some new features to a large (and dirty) codebase which has virtually *NO* unit-testing code?
body: <p><a href="https://rads.stackoverflow.com/amzn/click/com/0201485672" rel="noreferrer" rel="nofollow noreferrer">Martin Fowler</a> says that we should do refactoring before adding new features (given that the original program is not well-structured).</p>
  
  <p>So we all want to refactor this <em>dirty</em> codebase, that's for sure. We also know that without unit-testing code it's very easy to introduce subtle bugs.</p>
  
  <p>But it's a large codebase. Adding a complete suite of tests to it seems impracticable.</p>
  
  <p>What would you do in this case?</p>