Python模拟，预期的str实例MagicMock已找到

我正在尝试将Mock与Django一起使用有两件事：1.获取一个用户（我们有一个自定义后端，可以进行我要避免的网络调用）2.模拟出另一种获取令牌的方法，该令牌用于通过网络重置密码。

这是测试：

@patch('core.views.KagisoUser')
def test_forgot_password_sends_reset_email(self, MockKagisoUser):  # noqa
    email = '[email protected]'
    user = MagicMock()
    user.email = email
    user.generate_reset_password_token.return_value = email
    MockKagisoUser.objects.first.return_value = user
    data = {'email': email}
    client = Client()

    response = client.post('/forgot_password/', data, follow=True)
    message = list(response.context['messages'])[0].message

    assert response.status_code == 200
    assert 'You will receive an email with reset instructions shortly' \
        == message

    assert len(mail.outbox) == 1
    assert mail.outbox[0].to[0] == email
    assert mail.outbox[0].subject == 'Password Reset'
    assert mail.outbox[0].alternatives[0]  # HTML body

我收到此错误：

self = <django.core.mail.message.EmailMultiAlternatives object at 0x7f52eacd3390>

        def message(self):
            encoding = self.encoding or settings.DEFAULT_CHARSET
            msg = SafeMIMEText(self.body, self.content_subtype, encoding)
            msg = self._create_message(msg)
            msg['Subject'] = self.subject
            msg['From'] = self.extra_headers.get('From', self.from_email)
    >       msg['To'] = self.extra_headers.get('To', ', '.join(self.to))
    E       TypeError: sequence item 0: expected str instance, MagicMock found

这是实现：

def forgot_password(request):
    reset_message = 'You will receive an email with reset instructions shortly'
    not_found_message = 'We could not find a user for that email address'

    if request.method == 'POST':
        form = forms.ForgotPasswordForm(request.POST)

        if form.is_valid():
            email = form.cleaned_data['email']
            user = KagisoUser.objects.filter(email=email).first()

            if user:
                print(user.email)
                token = user.generate_reset_password_token()
                url = request.build_absolute_uri(reverse('reset_password'))
                message = render_to_string(
                    'core/emails/reset_password.html',
                    {
                        'url': url,
                        'token': token,
                        'user_id': user.id
                    }
                )
                send_mail(
                    'Password Reset',
                    '',
                    '[email protected]',
                    [user.email],
                    html_message=message
                )
                messages.success(request, reset_message)
                return HttpResponseRedirect('/')
            else:
                messages.error(request, not_found_message)
                return HttpResponseRedirect(reverse('forgot_password'))
    else:
        form = forms.ForgotPasswordForm()

    return render(
        request,
        'core/auth/forgot_password.html',
        {'form': form}
    )

我究竟做错了什么？