mocking-strategies

Isolate external dependencies in Python tests using unittest.mock by patching module boundaries with patch, MagicMock with spec, side_effect, and return_value to replace database or API calls. Pytest's monkeypatch is also supported for modifying attributes during test runs.

The best way to mock APIs and databases in JavaScript testing is using jest.mock or vi.mock to replace modules. You can also use manual mocks, dependency injection, or msw to isolate external HTTP requests and control return values.

You should not use mocking when testing core logic or simple pure functions, as over-mocking can hide integration failures. Follow MUST NOT guidelines to avoid replacing internal code and only mock external dependencies like databases or APIs to maintain test reliability.

Verify mock calls and side effects in Python by inspecting MagicMock attributes like call_count and assert_called_with, and in JavaScript by using jest or vi mock verification methods. Ensure spec-enabled mocks are used to prevent calling non-existent methods during verification.

Yes, this mocking approach works with both pytest and Jest frameworks. It provides specific patterns for Python using unittest.mock and pytest monkeypatch, alongside JavaScript patterns for Jest and Vitest using jest.mock, vi.mock, and msw.