Wait mongo connection before test express controller/route with supertest

example.js

var request = require('supertest'),
      mongoose = require('mongoose'),
      app = require('../../../../server');

describe('GET /api/transactions/import', function(){
  before(function (done) {
    mongoose.connection.on('open', done);
  });

  it('respond with json', function(done){
    request(app)
      .get('/api/transactions/import')
      .expect(200)
      .end(function(err, res){
        if (err) return done(err);
        done();
      });
  });
});

wait-mongo-connection-before-tests.js

before(function (done) {
  mongoose.connection.on('open', done);
});