Testing Model Properties and Methods

+15 Mana ✨
Model Methods(DOCUMENTATION)

Introduction

Models often contain business logic in properties and methods. Testing these ensures your domain logic works correctly.

Key Concepts

Property: Computed attribute using @property decorator.

Model Method: Instance or class method with business logic.

Deep Dive

Testing Properties

python
class ArticlePropertyTests(TestCase):
    def test_word_count_property(self):
        article = Article(body='one two three four five')
        self.assertEqual(article.word_count, 5)
    
    def test_reading_time_property(self):
        # 200 words = 1 minute reading time
        article = Article(body=' '.join(['word'] * 400))
        self.assertEqual(article.reading_time, 2)
    
    def test_is_published_property(self):
        article = Article(status='published')
        self.assertTrue(article.is_published)
        
        draft = Article(status='draft')
        self.assertFalse(draft.is_published)

Testing Instance Methods

python
class ArticleMethodTests(TestCase):
    def test_publish_method(self):
        article = Article.objects.create(title='Test', status='draft')
        article.publish()
        
        self.assertEqual(article.status, 'published')
        self.assertIsNotNone(article.pub_date)
    
    def test_archive_method(self):
        article = Article.objects.create(title='Test', status='published')
        article.archive()
        
        article.refresh_from_db()
        self.assertEqual(article.status, 'archived')

Testing Class Methods

python
class ArticleClassMethodTests(TestCase):
    def test_published_count(self):
        Article.objects.create(title='A', status='published')
        Article.objects.create(title='B', status='published')
        Article.objects.create(title='C', status='draft')
        
        self.assertEqual(Article.published_count(), 2)

Real World Context

Model properties and methods often contain critical business logic -- calculating prices, determining user permissions, or formatting display data. These are fast to test (no HTTP overhead) and provide high confidence in your domain logic. Testing edge cases in properties prevents subtle bugs that appear only with unusual data.

Common Pitfalls

  1. Not testing edge cases in properties: What does word_count return for an empty string? What about a single word?
  2. Forgetting refresh_from_db after method calls: Methods that call save() update the database but not the in-memory object.
  3. Testing computed properties with stale data: If a property depends on related objects, ensure those objects are up to date.

Best Practices

  1. Test edge cases: Empty strings, None values, boundary conditions.
  2. Use refresh_from_db(): After operations that modify the database.
  3. Test return values: Verify methods return expected values.

Summary

Test model properties and methods as units of business logic. Verify both happy paths and edge cases. Use refresh_from_db() to ensure database state is current.

✓ Completed