How to set cookie with django-webtest

I am trying to test piece of code which depends on cookie. code in question is like this:

try:
    json_string = urllib.unquote(request.COOKIES['add_global_user']).decode('utf-8')
    initial = json.loads(json_string)
    if 'company_name' in initial.keys():
        company_type = get_company_type(initial['company_name'])

    download_notifications = initial.get('download_notifs', False)

    form = AddUserForm(request=request, initial=initial)
    form.fields['needs_lms_access'].initial = True
    response = render(request, "accounts/users/adduserglobal.html", locals())
    response.delete_cookie("add_global_user", path="/accounts/user/add")
    return response
except KeyError:
    _logger.debug("KeyError, no add_global_user cookie found, displaying form w/o data")
    form = AddUserForm(request=request, initial={'first_name':'keyerror'})
except ValueError:
    _logger.debug("ValueError, No valid JSON could be decoded, displaying form w/o data; %s",
                  request.COOKIES['add_global_user'])
    form = AddUserForm(request=request, initial={'first_name':'valueerror'})
except Exception as e:
    _logger.debug("Exception occurred while retrieving form data from cookie, %s", str(e))
    form = AddUserForm(request=request, initial={'first_name':str(e)})

I am using django-webtest to write test cases, my attempt to test is:

class TestAddUser(WebTest):
    def test_bound_form_with_cookie(self):
        company = G(Company)
        user = G(User, email='superuser@tarams.com', is_superuser=True)

        cookie_dict = {
            "email": "email",
            "first_name": "3rd",
            "last_name": "2018",
        }

        self.app.set_cookie("add_global_user", json.dumps(cookie_dict))
        response = self.app.get('/accounts/user/add/', user=user)
        assert response.context['form'].initial['email'] == 'email'

running it django-webtest calls set_cookie method of DjangoTestApp whose source code is:

def set_cookie(self, *args, **kwargs):
        self.extra_environ = self._update_environ(self.extra_environ)
        return super(DjangoTestApp, self).set_cookie(*args, **kwargs)

and it throws error:

AttributeError: 'super' object has no attribute 'set_cookie'

I have given considerable time but could not find anything or workaround. Help appreciated. Thanks