title: Skipping unit tests or at least showing warnings from them
body: <p>I need to test code that fetches and processes some data from standard C library. However, this data may not be installed at any particular system. So at the start of each test I detect whether the data is installed and skip the test.</p>
  
  <p>It's easy to wrap the test in an if, but since the code that tests whether the test is possible may itself fail, I need to at least know that the tests were skipped. I know I <a href="https://stackoverflow.com/questions/25106554/println-doesnt-work-in-rust-unit-tests">can't simply use <code>println!</code></a> and I don't want to have to remember to pass <code>--nocapture</code> every time I test (and I want to see the warnings in the Travis log; Travis virtuals don't have all the data).</p>