title: How to test functions cdef'd in Cython?
body: <p>I have a .pyx file in which I define some functions, e.g.</p>
  
  <pre><code>cdef double foo(double a) nogil:
      return 3. * a
  </code></pre>
  
  <p>How could I unit test the behavior of such functions outside the pyx file? Since they are cdef'd, I am not able to simply import them...</p>