tions();

          expect(options.headers).to.be.ok;
          expect(options.headers['custom-header']).to.be.an('string');
          expect(options.headers.hasOwnProperty('custom-header')).to.be.equal(
              true);
        });

        test('non-objects in headers are not applied', function() {
          ajax.headers = 'invalid';
          var options = ajax.toRequestOptions();

          expect(Object.keys(options.headers).length).to.be.equal(0);
        });
      });

      suite('when url isn\'