♻️(backend) fallback to email identifier when no name (#1298)

In the UserlightSerializer, if the user has no short_name or full_name,
we have no info about the user. We decided to use the email identifier
and slugify it to have a little bit information.

src/backend/core/tests/serializers/test_user_light_serializer.py

@@ -0,0 +1,44 @@
+"""Test user light serializer."""
+
+import pytest
+
+from core import factories
+from core.api.serializers import UserLightSerializer
+
+pytestmark = pytest.mark.django_db
+
+
+def test_user_light_serializer():
+    """Test user light serializer."""
+    user = factories.UserFactory(
+        email="test@test.com",
+        full_name="John Doe",
+        short_name="John",
+    )
+    serializer = UserLightSerializer(user)
+    assert serializer.data["full_name"] == "John Doe"
+    assert serializer.data["short_name"] == "John"
+
+
+def test_user_light_serializer_no_full_name():
+    """Test user light serializer without full name."""
+    user = factories.UserFactory(
+        email="test_foo@test.com",
+        full_name=None,
+        short_name="John",
+    )
+    serializer = UserLightSerializer(user)
+    assert serializer.data["full_name"] == "test_foo"
+    assert serializer.data["short_name"] == "John"
+
+
+def test_user_light_serializer_no_short_name():
+    """Test user light serializer without short name."""
+    user = factories.UserFactory(
+        email="test_foo@test.com",
+        full_name=None,
+        short_name=None,
+    )
+    serializer = UserLightSerializer(user)
+    assert serializer.data["full_name"] == "test_foo"
+    assert serializer.data["short_name"] == "test_foo"