Challenge 2: Write a View Test With the Test Client — Possible Solution
====================================================================

# catalog/tests.py

from django.test import TestCase
from .models import Author, Book

class BookDetailViewTests(TestCase):
    def setUp(self):
        self.author = Author.objects.create(name="N.K. Jemisin")
        self.book = Book.objects.create(
            title="The Fifth Season",
            author=self.author,
            price=14.99,
        )

    def test_book_detail_returns_200(self):
        response = self.client.get(f"/books/{self.book.pk}/")
        self.assertEqual(response.status_code, 200)

    def test_book_detail_uses_correct_template(self):
        response = self.client.get(f"/books/{self.book.pk}/")
        self.assertTemplateUsed(response, "catalog/book_detail.html")

    def test_book_detail_contains_title(self):
        response = self.client.get(f"/books/{self.book.pk}/")
        self.assertContains(response, "The Fifth Season")

    def test_book_detail_404_for_missing_book(self):
        response = self.client.get("/books/99999/")
        self.assertEqual(response.status_code, 404)

WHY THIS WORKS
--------------
- self.client.get(f"/books/{self.book.pk}/") builds the URL using the
  actual primary key of the book created in setUp() — using an f-string
  with self.book.pk (rather than a hardcoded "/books/1/") means the test
  keeps working even if Django's auto-incrementing IDs don't happen to
  start at 1 in a given test run.
- assertTemplateUsed and assertContains check two DIFFERENT things that
  could each fail independently: assertTemplateUsed confirms the correct
  TEMPLATE rendered (catching a view that accidentally renders the wrong
  page while still returning 200), while assertContains confirms the
  actual page CONTENT includes the expected text — a view could use the
  right template but still fail to pass the right context data into it.
- test_book_detail_404_for_missing_book uses a primary key (99999) that's
  extremely unlikely to exist, verifying the view correctly returns a 404
  for a nonexistent book rather than crashing with an unhandled
  DoesNotExist exception — a common real bug when a view uses
  Book.objects.get(pk=book_id) directly instead of
  get_object_or_404(Book, pk=book_id).