Pytest: Mocking - why?

• Testing environment that does not depend on external systems.
• Faster tests (mock remote calls, mock whole databases, etc.)
• Fake some code/application/API that does not exist yet.
• Test error conditions in a system not under our control.

• TDD, unit tests
• Spaghetti code
• Simulate hard to replicate cases
• 3rd party APIs or applications