What is the difference between Stub and Mock?
Updated Apr 28, 2026
Short answer
A Stub is a minimal implementation for indirect inputs; a Mock is a pre-programmed object that verifies indirect outputs/expectations.
Deep explanation
Intermediate testing involves strategy and automation. TDD changes the workflow to 'Test First', which improves code quality and design. Integration testing moves away from units to verify the 'contract' between services. At this level, understanding mocks and stubs is vital for isolating dependencies.
Real-world example
Automating a checkout flow using Selenium or Playwright where the database is mocked to speed up execution.
Common mistakes
- Writing 'Brittle' UI tests that break every time a CSS class changes.
Follow-up questions
- What is 'shifting left' in testing?