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Testing

pytest Fundamentals

Writing tests with pytest — the standard Python testing framework

Interview: Expected at all professional levels

Last Updated: June 12, 2026 • 8 min read

pytest is the de facto standard testing framework for Python. It provides powerful fixtures, parameterization, and a simple assertion-based syntax.

Why pytest over unittest

  • Simple assertions: Use plain assert instead of assertEqual, assertTrue
  • Fixtures: Reusable setup/teardown code via dependency injection
  • Parameterization: Run the same test with different inputs
  • Plugins: Rich ecosystem (pytest-cov, pytest-django, pytest-asyncio)

Use Cases

Unit testing business logic

Integration testing with database fixtures

API endpoint testing with mock dependencies

Parameterized tests for edge case coverage

Common Mistakes

Not using fixtures — duplicating setup code across tests

Forgetting to test the error path (exceptions, edge cases)

Mocking too much — prefer integration tests for critical paths

Not using pytest-cov to measure test coverage