Why is testing divided into separate stages?

Testing is divided into stages due to the need to ensure comprehensive quality checks at different levels of detail and at various points in the software development lifecycle. This allows:

1. Efficient defect detection: Defects found early are cheaper and easier to fix.
2. Systematic approach: Software testing occurs from small components to the interaction of all parts of the system.
3. Distribution of responsibilities: Different stages can be performed by different teams or specialists (developers, testers).
4. Risk reduction: Gradual testing reduces the risk of releasing a defective product.
5. Compliance with requirements/specifications: At each stage, the fulfillment of certain requirements and characteristics is checked.

The main stages include:

• Unit testing: Checking the smallest isolated parts of code (functions, methods). Usually performed by developers.
• Integration testing: Checking the interaction between different modules or components.
• System testing: Comprehensive testing of the system as a whole, including functional and non-functional requirements (performance, security, usability, etc.).
• Acceptance testing: Checking the system for compliance with the end user's or customer's requirements. May include alpha and beta testing.