title: Mock HTTP server that performs content negotiation
body: <p>I normally use Python's <code>http.server</code> to mock an HTTP server but this time I need the server to perform content negotiation.</p>
  
  <p>I just need it to return an error if it cannot match the Accept header. Python's server ignores the header.</p>
  
  <p>The way to run the server could be in a thread or in a separate process such as by running <code>python -m http.server</code>.</p>