Introduction to Software Testing

What is Software Testing?

Software testing is the process of evaluating a system to check whether it meets the specified requirements and to find defects. Testing answers two questions: does the software do what it should, and does it avoid doing what it should not?

Why Software Testing is Important

• Quality - catches bugs before users do, protecting brand trust.
• Cost - a bug found in requirements costs 1x to fix; in production it costs 100x (Boehm law).
• Security - testing exposes SQL injection, XSS and auth flaws early.
• Confidence - regression suites let teams release weekly without fear.

Error vs Bug vs Defect vs Failure

• Error - a human mistake (wrong logic in code).
• Defect/Bug - the deviation in the software caused by the error.
• Failure - the observable wrong behaviour when the defect executes.

QA vs QC vs Testing

• QA (Quality Assurance) - process-oriented: prevents defects (audits, standards, reviews).
• QC (Quality Control) - product-oriented: finds defects (testing, inspections).
• Testing - executes the software to detect defects; it is a subset of QC.

Tester Roles and Responsibilities

• Understand requirements and write test cases and test data.
• Execute tests, log clear bug reports, and retest fixes.
• Build and maintain automation suites and CI pipelines.
• Report quality metrics (pass rate, defect density, leakage) to stakeholders.

Key Points

• Testing shows the presence of bugs, never their absence (Dijkstra).
• QA prevents, QC detects, testing executes.
• Earlier testing is exponentially cheaper than late fixes.