✅(tests) fix tests after adding slugs to domains

- slug readonly on admin
- fix test to expect slug in payload, when retrieving a domain

src/backend/mailbox_manager/tests/api/mail_domain/test_api_mail_domains_retrieve.py

@@ -66,6 +66,7 @@ def test_api_mail_domains__retrieve_authenticated_related():
     assert response.json() == {
         "id": str(domain.id),
         "name": domain.name,
+        "slug": domain.slug,
         "created_at": domain.created_at.isoformat().replace("+00:00", "Z"),
         "updated_at": domain.updated_at.isoformat().replace("+00:00", "Z"),
     }

src/backend/mailbox_manager/tests/test_models_maildomain.py

@@ -3,6 +3,7 @@ Unit tests for the MailDomain model
 """
 
 from django.core.exceptions import ValidationError
+from django.utils.text import slugify
 
 import pytest
 
@@ -10,7 +11,6 @@ from mailbox_manager import factories
 
 pytestmark = pytest.mark.django_db
 
-
 # NAME FIELD
 
 
@@ -24,3 +24,11 @@ def test_models_mail_domain__domain_name_should_not_be_null():
     """The domain name field should not be null."""
     with pytest.raises(ValidationError, match="This field cannot be null."):
         factories.MailDomainFactory(name=None)
+
+
+def test_models_mail_domain__slug_inferred_from_name():
+    """Passed slug is ignored. Slug is automatically generated from name."""
+
+    name = "N3w_D0main-Name$.com"
+    domain = factories.MailDomainFactory(name=name, slug="something else")
+    assert domain.slug == slugify(name)