title: With testthat, where to place a custom skip function?
body: <p>Where to place this function:</p>
  
  <pre><code>skip_on_any &lt;- function() {
    skip_on_cran()
    skip_on_travis()
    skip_on_appveyor()
    skip_on_bioc()
  }
  </code></pre>
  
  <p>So that I can use it within any of my test files.</p>