Choose normal and abnormal test data
Test a requirement with representative valid data and invalid inputs that should be rejected.
This sequence follows Cambridge IGCSE Computer Science 0478, 2026–2028 syllabus Version 6. It covers subject content Topic 7 only. The separately published 2029–2031 syllabus is not mapped here. Practice is original, self-checked and does not award an official Cambridge grade. Full timed papers and human subject-teacher review remain outstanding.
Before you begin
- No programming language is required. Be comfortable with place value and multiplication; each lesson introduces the computer-science notation it uses.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
For a mark from 0 to 100, is 65 a normal valid value?
What you will learn
- Define normal test data
- Define abnormal test data
- Choose values with expected results
Test data checks specified behaviour
Normal test data is valid and typical input that should be accepted. Abnormal data is invalid input that should be rejected or handled safely.
Apply and check the rule
Choose test values from the requirement and state the expected result before running the program. Testing should cover important branches, not just show that the program can process one convenient example.
Pause and explain
Which is abnormal data for an integer field?
Worked example
A quantity must be an integer from 1 to 20. Give normal and abnormal test data.
Show the worked solution
- A typical valid value such as 8 is normal.
- A value such as 0 violates the range.
- Text such as “many” violates the required type.
Answer Normal: 8, accepted. Abnormal: 0 or “many”, rejected with a suitable message.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A username must contain 5–12 characters. Give one normal and one abnormal test value with expected results.
Give me a hint
Choose one typical acceptable length and one value outside the rule.
Compare my reasoning
- “Mila7” has five characters and is valid.
- “ab” is too short.
- The program should accept the first and reject the second.
Normal: Mila7, accepted. Abnormal: ab, rejected for being too short.
Look for these in your work
- Valid normal
- Invalid abnormal
- Expected results
A test plan contains only values that the program should accept. What important behaviour has not been tested?
Give me a hint
Consider how the program responds to invalid input.
Compare my reasoning
- The plan checks only valid routes.
- It does not show whether unsuitable data is rejected safely.
- Add abnormal inputs and check the resulting message or recovery.
It has not tested error handling. Include invalid inputs and verify that the program rejects or handles them as specified.
Look for these in your work
- Coverage gap
- Risk
- Additional test
A program rejects an invalid age but crashes without a message. Explain why the test should be recorded as a failure even though the value was not accepted.
Give me a hint
The required response includes safe handling, not merely rejection.
Compare my reasoning
- The input was correctly not accepted.
- A crash is not a clear or controlled response.
- Record the failure and amend the error-handling path.
The test fails because the program should handle abnormal input safely and explain the problem, not crash. Amend and retest that path.
Look for these in your work
- Input outcome
- Handling quality
- Correction
Common mistakes
- Calling the smallest accepted input abnormal
- Testing invalid data without checking that it is handled clearly
What can you explain now?
What should happen to abnormal test data?
Compare with the explanation
It should be rejected or handled according to the specification
The expected outcome should be defined before testing.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
How do normal and abnormal test data differ?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.