Correct sinon usage?

gistfile1.js

'use strict';

var sinon = require('sinon');
var request = require('request');

describe('standalone-issuer', function() {

  var rPost;

  beforeEach(function(done) {
    rPost = sinon.stub(request, 'post');
    rPost.withArgs({uri:'somewhere',body:'something'}, sinon.match.any)
      .yields(null, {statusCode: 200}, JSON.stringify({someData: 'something!'}));
    rPost.withArgs({uri:'somewhere',body:'somethingElse'}, sinon.match.any)
      .yields(null, {statusCode: 400}, JSON.stringify({someData: 'something!'}));
    done();
  });

  afterEach(function(done) {
    request.post.restore();
    done();
  });
  it('should return 200', function(done) {
    request.post({uri:'somewhere',body:'something'}, function(err, res, body) {
      should.not.exist(err);
      res.statusCode.should.equal(200);
      sinon.assert.calledWith(rPost, {uri:'somewhere',body:'something'}, sinon.match.any);
      done();
    })
  });
  it('should return 400', function(done) {
    request.post({uri:'somewhere',body:'somethingElse'}, function(err, res, body) {
      should.not.exist(err);
      res.statusCode.should.equal(400);
      sinon.assert.calledWith(rPost, {uri:'somewhere',body:'somethingElse'}, sinon.match.any);
      done();
    })
  });
});