How do I mock dependencies in unit tests?

How do I mock dependencies in unit tests?

Mocking dependencies in unit tests allows you to isolate the unit of work and test it independently. You can use libraries like Mockito in Java or unittest.mock in Python.

Can you show me an example in Python?

Sure! Here's a simple example using unittest.mock:

from unittest import TestCase
from unittest.mock import Mock

class MyService:
    def __init__(self, dependency):
        self.dependency = dependency

    def perform_action(self):
        return self.dependency.do_something()

class TestMyService(TestCase):
    def test_perform_action(self):
        mock_dependency = Mock()
        mock_dependency.do_something.return_value = 'mocked result'
        service = MyService(mock_dependency)
        result = service.perform_action()
        self.assertEqual(result, 'mocked result')

This tests MyService without relying on the actual implementation of dependency.

What if I want to mock multiple dependencies?

You can create multiple mock objects for each dependency and pass them to your class. Just ensure each mock is configured as needed for your tests.

Are there any best practices for mocking?

Yes! Some best practices include:

1. Mock only what you need to isolate the unit.
2. Avoid over-mocking, which can lead to brittle tests.
3. Keep your mocks simple and focused on the behavior you want to test.