Fundamentals of Testing
Core concepts
Testing is the process of evaluating a work product to find defects and provide information about quality. Its objectives vary by context: find defects, gain confidence, provide decision information, prevent defects, and satisfy contractual or regulatory requirements. Quality assurance is process-oriented and preventive; quality control is product-oriented and includes testing. Distinguish error (human mistake), defect (fault in a work product), and failure (incorrect behavior during execution). A defect may never cause a failure, and a failure can have a cause outside the tested component.
The test process groups activities: planning; monitoring and control; analysis; design; implementation; execution; and completion. Test conditions are what to test; test cases add inputs, preconditions, and expected results; test procedures order test cases. The seven principles matter: testing shows presence of defects, exhaustive testing is impossible, early testing saves cost, defects cluster, tests wear out (pesticide paradox), testing is context dependent, and absence of errors is a fallacy. Independence helps but does not guarantee better testing.
Traps
Questions often equate testing with debugging, QA with testing, or defect with failure. Testing does not prove correctness; it reduces risk. More testing is not always better without risk focus.
Worked example
A developer types > instead of >= in a length check. The typing slip is an error; the wrong operator in code is a defect; a 6-character name being rejected is a failure. A test observes the failure; debugging locates and fixes the defect.
Rule of thumb: report observed behavior and evidence, not blame.