Can you explain the main concepts and principles of the fundamental software testing theory?

The fundamental theory of software testing is based on several key principles:

• Testing shows the presence of defects, but not their absence. Even if tests pass successfully, it does not guarantee that there are no errors in the program.
• Exhaustive testing is impossible. Complete coverage of all possible scenarios is often unfeasible due to the vast number of combinations.
• Early testing reduces the cost of fixing errors. The earlier defects are identified, the cheaper it is to fix them.
• Testing should be independent. Independence of testers helps identify errors that may have been overlooked by developers.
• Testing is based on requirements. Tests should verify that the program complies with the specified requirements.

Main concepts include:

• Test cases and test plans: describe what and how to check.
• Types of testing: functional, non-functional, regression, load testing, etc.
• Testing methods: black box (without knowledge of internal structure), white box (with code analysis), gray box.

These principles help systematize the testing process and improve software quality.