span></code>. When you run these provided tests, you will see that the tests for the <code class="language-c++ highlighter-rouge"><span class="n">lettersOnly</span></code> function all pass. From this, you might conclude that the function is good to go. However, there is a problem lurking within the code that has yet to be uncovered!</p>

<p>Review our provided test cases to see what sorts of inputs we tested, and, more importantly, what sorts of inputs we <em>didn't</em> test.  Brainstorm what those missin