Object of type date is not JSON serializable (error in tests.py)

Question

I wrote this view to register with the user's phone and the view itself works fine

But in test def test_signup_phone_post (self)

For response = self.client.post (reverse ('signup_phone'), self.user, follow = True)

This gives the error: TypeError: Object of type date is not JSON serializable

views.py

class SignupPhoneView(View):
    def get(self, request):
        form = SignupPhoneForm()
        return render(request, 'user/signup_phone.html', {'form': form})

    def post(self, request):
        form = SignupPhoneForm(request.POST)
        if User.objects.filter(username=request.POST.get("username") + "@mail.com"):  # If username already exists
            logger_warn.warning(f'class SignupPhoneView, {request.POST.get("username")}, Registration exists')
            return redirect("/user/signup-phone/", messages.error(request, "Registration exists"))
        elif form.is_valid():
            token = random.randint(100000, 999999)
            kave_negar_token_send(form.cleaned_data['recovery_phone'], token)
            code = OtpCode.objects.create(phone_number=form.cleaned_data['recovery_phone'], code=token)
            print(code)
            request.session['signup_info'] = {
                'username': form.cleaned_data['username'],
                'password': form.cleaned_data['password'],
                'first_name': form.cleaned_data['first_name'],
                'last_name': form.cleaned_data['last_name'],
                'birthday': form.cleaned_data['birthday'],
                'gender': form.cleaned_data['gender'],
                'country': form.cleaned_data['country'],
                'recovery_phone': form.cleaned_data['recovery_phone']
            }
            messages.success(request, f'{request.POST.get("username")} please enter your verification code')
            return redirect("/user/phone-verify/")
        else:
            logger_error.error(f'class SignupEmailView, {request.POST.get("username")}, Registration failed')
            messages.error(request, "Registration failed")
            return redirect("/user/signup-phone/")

tests.py

class SignupPhoneTest(TestCase):
    def setUp(self):
        self.user = {
            'username': 'testuser',
            'password': '7895146',
            'recovery_phone': '09874563215',
            'first_name': 'lina',
            'last_name': 'wong',
            'birthday': '01/10/2000',
            'gender': 'f',
            'country': 'England'
        }

    def test_signup_phone_page_url(self):
        response = self.client.get("/user/signup-phone/")
        self.assertEqual(response.status_code, 200)
        self.assertTemplateUsed(response, template_name='user/signup_phone.html')

    def test_signup_phone_post(self):
        response = self.client.post(reverse('signup_phone'), self.user, follow=True)
        self.assertEqual(response.status_code, 200)
        self.assertEqual(response.redirect_chain, [(reverse('phone_verify'), 302)])