Add unit test

src/registrar/models/domain_request.py

@@ -9,6 +9,7 @@ from django.db import models
 from django_fsm import FSMField, transition  # type: ignore
 from django.utils import timezone
 from registrar.models.domain import Domain
+from registrar.models.federal_agency import FederalAgency
 from registrar.models.utility.generic_helper import CreateOrUpdateOrganizationTypeHelper
 from registrar.utility.errors import FSMDomainRequestError, FSMErrorCodes
 
@@ -752,7 +753,7 @@ class DomainRequest(TimeStampedModel):
         notification."""
 
         if self.federal_agency is None:
-            self.federal_agency = "Non-Federal Agency"
+            self.federal_agency = FederalAgency.objects.filter(agency="Non-Federal Agency").first()
             self.save()
 
         # create the domain

src/registrar/tests/test_models.py

@@ -12,6 +12,7 @@ from registrar.models import (
     DraftDomain,
     DomainInvitation,
     UserDomainRole,
+    FederalAgency,
 )
 
 import boto3_mocking
@@ -75,6 +76,26 @@ class TestDomainRequest(TestCase):
         with less_console_noise():
             return self.assertRaises(Exception, None, exception_type)
 
+    def test_federal_agency_set_to_non_federal_on_approve(self):
+        """Ensures that when the federal_agency field is 'none' when .approve() is called,
+        the field is set to the 'Non-Federal Agency' record"""
+        domain_request = completed_domain_request(
+            status=DomainRequest.DomainRequestStatus.IN_REVIEW,
+            name="city2.gov",
+            federal_agency=None,
+        )
+
+        # Ensure that the federal agency is None
+        self.assertEqual(domain_request.federal_agency, None)
+
+        # Approve the request
+        domain_request.approve()
+        self.assertEqual(domain_request.status, DomainRequest.DomainRequestStatus.APPROVED)
+
+        # After approval, it should be "Non-Federal agency"
+        expected_federal_agency = FederalAgency.objects.filter(agency="Non-Federal Agency").first()
+        self.assertEqual(domain_request.federal_agency, expected_federal_agency)
+
     def test_empty_create_fails(self):
         """Can't create a completely empty domain request.
         NOTE: something about theexception this test raises messes up with the