What is the principle of defect clustering or clustering?

Defect Clustering is one of the seven fundamental principles of software testing, asserting that a small number of modules or components contain the majority of identified defects. In other words, defects are unevenly distributed.

This does not mean that only these "problematic" areas should be tested. Rather, this principle emphasizes the importance of analyzing defect history and focusing testing efforts on parts of the system where defects are most frequently found.

Reasons for clustering can vary:

• Complexity of the code or business logic of the module.
• Frequent changes in the component.
• Experience and skills of the developer who worked on the module.
• Insufficient test coverage previously.

Applying the principle in practice:

• Using data from defect tracking systems (Jira, Azure DevOps, etc.) to identify "hot" spots.
• Adjusting test plans and strategies, paying more attention to problematic modules.
• Conducting additional regression testing in areas with high defect density.
• Prioritizing automation of tests for such modules.