test: Enhance test coverage for the business application

This commit expands the test suite for the `business` application, improving validation and model testing.

Key additions include:
- **Authentication:** Added tests to `InvalidCompanyRegistrationTestCase` and `InvalidCompanyAuthenticationTestCase` to handle cases like missing email on  creation and sign-in with an invalid email.
- **Models:** Created `promo_code/business/tests/promocodes/test_models.py`  to verify the `__str__` representations for the `Company`, `Promo`, and
     `PromoCode` models.
- **Promo Creation:** Added validation tests in `TestPromoCreate` to ensure that `promo_common` is provided for 'COMMON' promos and `promo_unique` is
     provided for 'UNIQUE' promos.

Author: RandomProgramm3r

promo_code/business/tests/auth/test_validation.py

@@ -90,6 +90,17 @@ def test_short_company_name(self):
             rest_framework.status.HTTP_400_BAD_REQUEST,
         )
 
+    def test_create_company_missing_email_fiels(self):
+        with self.assertRaisesMessage(
+            ValueError,
+            'The Email must be set',
+        ):
+            business.models.Company.objects.create_company(
+                name=self.valid_data['name'],
+                password=self.valid_data['password'],
+                email=None,
+            )
+
 
 class InvalidCompanyAuthenticationTestCase(
     business.tests.auth.base.BaseBusinessAuthTestCase,
@@ -132,3 +143,24 @@ def test_signin_invalid_password(self):
             response.status_code,
             rest_framework.status.HTTP_401_UNAUTHORIZED,
         )
+
+    def test_signin_invalid_email(self):
+        business.models.Company.objects.create_company(
+            email=self.valid_data['email'],
+            name=self.valid_data['name'],
+            password=self.valid_data['password'],
+        )
+
+        data = {
+            'email': '[email protected]',
+            'password': self.valid_data['password'],
+        }
+        response = self.client.post(
+            self.company_signin_url,
+            data,
+            format='json',
+        )
+        self.assertEqual(
+            response.status_code,
+            rest_framework.status.HTTP_400_BAD_REQUEST,
+        )

promo_code/business/tests/promocodes/test_models.py

@@ -0,0 +1,53 @@
+import django.test
+
+import business.constants
+import business.models
+
+
+class CompanyModelTests(django.test.TestCase):
+    def test_company_str_representation(self):
+        company = business.models.Company.objects.create(
+            email='[email protected]',
+            name='My Awesome Company',
+        )
+        self.assertEqual(str(company), 'My Awesome Company')
+
+
+class PromoModelTests(django.test.TestCase):
+    def setUp(self):
+        self.company = business.models.Company.objects.create(
+            email='[email protected]',
+            name='TestCorp',
+        )
+        self.common_promo = business.models.Promo.objects.create(
+            company=self.company,
+            description='A common promo',
+            max_count=100,
+            used_count=50,
+            mode=business.constants.PROMO_MODE_COMMON,
+        )
+
+    def test_promo_str_representation(self):
+        expected_str = (
+            f'Promo {self.common_promo.id} ({self.common_promo.mode})'
+        )
+        self.assertEqual(str(self.common_promo), expected_str)
+
+
+class PromoCodeModelTests(django.test.TestCase):
+    def test_promo_code_str_representation(self):
+        company = business.models.Company.objects.create(
+            email='[email protected]',
+            name='TestCorp',
+        )
+        promo = business.models.Promo.objects.create(
+            company=company,
+            description='Unique codes promo',
+            max_count=10,
+            mode=business.constants.PROMO_MODE_UNIQUE,
+        )
+        promo_code = business.models.PromoCode.objects.create(
+            promo=promo,
+            code='UNIQUE123',
+        )
+        self.assertEqual(str(promo_code), 'UNIQUE123')

promo_code/business/tests/promocodes/validations/test_create_validation.py

@@ -306,6 +306,42 @@ def test_too_short_promo_common(self):
             rest_framework.status.HTTP_400_BAD_REQUEST,
         )
 
+    def test_missing_promo_common_field_for_common_promo(self):
+        payload = {
+            'description': 'Increased cashback 40% for new bank clients!',
+            'max_count': 100,
+            'target': {},
+            'active_from': '2028-12-20',
+            'mode': 'COMMON',
+        }
+        response = self.client.post(
+            self.promo_list_create_url,
+            payload,
+            format='json',
+        )
+        self.assertEqual(
+            response.status_code,
+            rest_framework.status.HTTP_400_BAD_REQUEST,
+        )
+
+    def test_missing_promo_unique_field_for_unique_promo(self):
+        payload = {
+            'description': 'Increased cashback 40% for new bank clients!',
+            'max_count': 100,
+            'target': {},
+            'active_from': '2028-12-20',
+            'mode': 'UNIQUE',
+        }
+        response = self.client.post(
+            self.promo_list_create_url,
+            payload,
+            format='json',
+        )
+        self.assertEqual(
+            response.status_code,
+            rest_framework.status.HTTP_400_BAD_REQUEST,
+        )
+
     @parameterized.parameterized.expand(
         [
             (