Introduction to Software Testing

Learning objectives#

• Explain what testing is and why it is needed
• Distinguish error, defect and failure
• Describe a tester’s daily work
• Understand the cost of finding bugs late

Explanation#

Testing is evaluating software to find defects and to gain confidence that it meets requirements and user needs.

A person makes an error (mistake) → it introduces a defect (bug) in the code or document → when executed it may cause a failure (wrong behaviour seen by users).

Testers read requirements, design test cases, execute them, report bugs, retest fixes and communicate quality risks to the team.

The later a bug is found, the more it costs: a requirement mistake caught in review costs minutes; the same bug in production can cost customers and money.

Code example: Error → defect → failure#

1Requirement: "Orders above ₹999 get free delivery."
2

3Error    Developer misreads it and writes:  if (total > 1000) freeDelivery = true;
4Defect   The condition excludes totals from ₹999.01 to ₹1000.
5Failure  A customer with a ₹1000 cart is charged ₹49 delivery and complains.
6

7Test that finds it: cart total = ₹1000 → expected: free delivery → actual: ₹49 charged

A single boundary test catches the defect before release instead of a customer finding it.

This example is illustrative. Copy or download it and run it in your own environment; the expected output is shown above.

Step-by-step explanation#

1. The requirement defines the expected behaviour.
2. A human error creates a defect in the code.
3. The defect causes a visible failure only for certain inputs.
4. A well-chosen test input reveals it early.

Real-world use case#

Common mistakes#

Best practices#

• Understand the requirement before testing
• Think like a user and like an attacker
• Report clearly and politely
• Start testing activities early

Remember this#

Practice exercise#

17 characters (expect rejected), 8 characters (accepted), 21 characters (rejected)

Mini quiz#

Want more? Practise all Manual Testing MCQs · Manual Testing interview questions

Related topics#

My notes#

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