title: Cargo says "test failed, to rerun pass '--lib" - What does it mean?
body: <p>What is cargo trying to tell me here with this final message? :</p>
  <p><code>error: test failed, to rerun pass '--lib'</code></p>
  <p>Even the Cargo book has test examples showing this exact final line, without explanation. It almost sounds like it is saying, &quot;If you don't pass --lib, we won't rerun the tests&quot; - Does it pull test results from a cache?</p>
  <p>If I add &quot;--lib&quot; to my command line, thus: <code>cargo test --features some_feature --lib</code>, it doesn't seem to do anything special.</p>
  <p>Doing some digging, I found <a href="https://github.com/ehuss/cargo/commit/c61efd8c39b58b2af17a3b9663a866fd17d295cd" rel="nofollow noreferrer">a Cargo code change</a> that seems to be trying to show &quot;{pkg_info}--lib&quot;</p>
  <p>So, what is Cargo trying to tell me? Something meaningful, or is it just a bug that confuses new users?</p>