How to unit test a form with a captcha field in django?

I would like to unit test a django view by sumitting a form. The problem is that this form has a captcha field (based on django-simple-captcha).

from django import forms
from captcha.fields import CaptchaField

class ContactForm(forms.forms.Form):
    """
    The information needed for being able to download
    """
    lastname = forms.CharField(max_length=30, label='Last name')
    firstname = forms.CharField(max_length=30, label='First name')
    ...
    captcha = CaptchaField()

The test code:

class ContactFormTest(TestCase):

    def test_submitform(self):
        """Test that the contact page"""
        url = reverse('contact_form')

        form_data = {}
        form_data['firstname'] = 'Paul'
        form_data['lastname'] = 'Macca'
        form_data['captcha'] = '28if'

        response = self.client.post(url, form_data, follow=True)

Is there any approach to unit-test this code and get rid of the captcha when testing?

Thanks in advance