fix: unit test book loans

loans/tests.py

 from django.test import TestCase
+from django.utils import timezone
+from django.contrib.auth.models import User
+from django.core.exceptions import ValidationError
+
+from .models import BookLoan, Book, Member
+
+
+class BookLoanModelTest(TestCase):
+
+    def setUp(self):
+        self.book = Book.objects.create(
+            title="Test Book",
+            author="Test Author",
+            publish_date=timezone.now(),
+            rating=5,
+        )
+        self.user = User.objects.create_user(
+            username="Test User", password="secret", is_staff=False
+        )
+        self.member = Member.objects.create(user=self.user)
+        self.loan_date = timezone.now()
+        self.due_date = self.loan_date + timezone.timedelta(days=14)
+
+    def test_book_loan_creation(self):
+
+        book_loan = BookLoan.objects.create(
+            book=self.book,
+            member=self.member,
+            loan_date=self.loan_date,
+            due_date=self.due_date,
+        )
+
+        self.assertEqual(book_loan.book, self.book)
+        self.assertEqual(book_loan.member, self.member)
+        self.assertEqual(book_loan.due_date, self.due_date)
+
+    def test_cascading_delete(self):
+        book_loan = BookLoan.objects.create(
+            book=self.book,
+            member=self.member,
+            loan_date=self.loan_date,
+            due_date=self.due_date,
+        )
+        book_loan_id = book_loan.id
+
+        self.book.delete()
+
+        with self.assertRaises(BookLoan.DoesNotExist):
+            BookLoan.objects.get(id=book_loan_id)