title: What are obsolete snapshots and snapshot files?
body: <p>I find the Jest Snapshot Summary a bit confusing. After running tests in one of our repositories, I get the following Summary:</p>
  
  <pre><code>Snapshot Summary
   › 2 snapshots written in 1 test suite.
   › 50 obsolete snapshot files found, re-run with `-u` to remove them.
   › 3 obsolete snapshots found, re-run with `-u` to remove them.
  </code></pre>
  
  <p>Snapshot testing means we compare the current tests' output against the output before our changes, to catch side effects.</p>
  
  <p>Hence, if I get it right, the summary means</p>
  
  <ul>
  <li>2 tests are new, no snapshots were available to compare against</li>
  <li>50 tests still provide the same output as before</li>
  <li>3 tests have been removed, but the snapshots are still around</li>
  </ul>
  
  <p>So running with <code>-u</code> would</p>
  
  <ul>
  <li>Update the time stamp for 50 snapshots, but not change their contents</li>
  <li>Delete the files for 3 snapshots that are useless</li>
  </ul>
  
  <p>Is that understanding correct?</p>