sinon_split.js

server.get('/bla', function(req, res) {
  // instead of adding the implementation here
});

// create a new function here 
function doBla(req, res) {
  // implementation here
});

// now add it to exports 
server.doBla = doBla;

// and in the actual endpoint just call the function
server.get('/bla', function(req, res) {
  doBla(req, res);
});

module.exports = server;