Testing Django Success Messages in Class-Based Views

I've identified several issues in your test code that could be causing the success message not to be captured. Let's address them one by one.

Main Issues

1. Username Mismatch in Login

The most obvious issue is that you're creating a user with username 'John' but trying to log in with username 'Ivan':

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# You create:
cls.test_user = User.objects.create_user(
    email='john123@gmail.com',
    username='John',
    password='Fiesta123'
)

# But you try to log in as:
login = self.client.login(username='Ivan', password='Fiesta123')

This login will fail, so your test is running with an unauthenticated user.

2. Form Data Format

When submitting form data for model instances, you need to provide the primary key, not the object itself:

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# Current approach (incorrect):
book_data = {
    'title': 'Great Expectations',
    'author': author,  # This should be author.pk
    'genre': genre     # This should be genre.pk
}

# Correct approach:
book_data = {
    'title': 'Great Expectations',
    'author': author.pk,
    'genre': genre.pk
}

3. Missing Required Fields

Your view defines more required fields than you're providing in the test:

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fields = ['title', 'author', 'genre', 'publisher', 'pages', 'cover', 'summary']

But your test only provides:

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book_data = {
    'title': 'Great Expectations',
    'author': author,
    'genre': genre
}

Corrected Test Code

Here's a corrected version of your test:

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class TestBookCreateView(MessagesTestMixin, TestCase):

    @classmethod
    def setUpTestData(cls):
        cls.test_user = User.objects.create_user(
            email='john123@gmail.com',
            username='John',
            password='Fiesta123'
        )
        cls.add_book_permission = Permission.objects.get(codename='add_book')

    def setUp(self):
        # Fix the username to match the created user
        login = self.client.login(username='John', password='Fiesta123')
        self.test_user.user_permissions.set([self.add_book_permission])

    def test_if_view_success_message_attached(self):
        author = Author.objects.create(
            first_name='Charles',
            last_name='Dickens'
        )

        genre = Genre.objects.create(
            genre='Novel'
        )
        
        publisher = Publisher.objects.create(name='Test Publisher')  # Add missing required fields
        
        book_data = {
            'title': 'Great Expectations',
            'author': author.pk,  # Use primary key
            'genre': genre.pk,    # Use primary key
            'publisher': publisher.pk,
            'pages': 400,
            'cover': '',  # Provide empty value if not required
            'summary': 'A classic novel'
        }

        response = self.client.post(reverse('add-book'), data=book_data, follow=True)
        self.assertMessages(response, 'Book successfully added')

Best Practices for Testing Messages in Django CBVs

1. Use the MessagesTestMixin: You're already doing this correctly.

2. Ensure proper authentication: Make sure the user is correctly logged in and has the necessary permissions.

3. Provide all required form data: Make sure all required fields are included in your test data.

4. Use primary keys for related objects: When submitting form data, use the primary keys of related objects, not the objects themselves.

5. Use follow=True in client.post(): This ensures that redirects are followed, which is important since messages are often set just before a redirect.

6. Check your middleware settings: Ensure that the messages middleware is included in your test settings:

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   MIDDLEWARE = [
       # ...
       'django.contrib.messages.middleware.MessageMiddleware',
       # ...
   ]

By addressing these issues, your test should be able to correctly capture and verify the success message from your CreateView.