What is incremental testing?

Incremental Testing is an integration testing strategy where system components or modules are tested after their sequential addition to already tested parts.

Key characteristics:

• Sequential addition: New modules are integrated one after another or in small groups.
• Re-testing: After adding a new module, integration testing is performed on the entire current build.
• Order dependence: The order of module integration is important.

Types of incremental testing:

• "Bottom-Up": Testing starts with the lowest-level modules that do not depend on others. Then higher-level modules that call them are added.
  • Advantages: Detects defects in critical low-level modules early.
  • Disadvantages: Main system modules (connecting everything together) are tested last.
• "Top-Down": Testing starts with high-level modules (e.g., user interface or main module). Lower-level functions not yet implemented are replaced with "stubs." Lower-level modules are tested and integrated gradually.
  • Advantages: Tests the execution flow close to real user scenarios early. Detects integration defects in core modules.
  • Disadvantages: Low-level modules are tested last. Requires stub development.
• "Sandwich" or "Hybrid": Combines "top-down" and "bottom-up" approaches. The main module is tested separately, lower-level modules are tested separately, and then these subsystems are integrated.
  • Advantages: Combines benefits of both approaches. Allows detection of defects at low levels and in main flows.

The goal of incremental testing is to detect defects arising from module interactions early in the integration process, making debugging easier compared to the "Big Bang" approach (testing all modules immediately after their development).