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Practise 29 exam-style questions on Test data for Cambridge IGCSE Computer Science (Paper 2). Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.
Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.
A program asks the user to enter a whole number from 1 to 50. The user types the word ten.
State the type of test data this is.
Abnormal data
The program expects a number, so text is the wrong data type and should be rejected. Data that should be rejected is abnormal data. Testing with it checks that the program does not crash or accept nonsense input.
Abnormal (test) data
Accept: erroneous data.
Explain why a program should be tested using abnormal data.
Abnormal data checks that the program rejects data that is invalid, so the validation routines work. It also shows that the program handles invalid input sensibly, for example by outputting an error message, instead of crashing or storing incorrect data.
Users will sometimes type the wrong thing, so a program must cope with it. Testing with abnormal data, such as values outside the range or of the wrong type, proves the validation catches these inputs. A program tested only with valid data might fail as soon as a user makes a mistake.
To check that invalid data is rejected / that the validation works
To make sure the program does not crash or produce incorrect results when invalid data is entered, e.g. it outputs a suitable error message instead
This algorithm should accept whole numbers from 1 to 12.
REPEAT
OUTPUT "Enter the number of guests (1 to 12)"
INPUT Guests
UNTIL Guests > 1 AND Guests <= 12When the algorithm is tested with extreme data, one of the tests shows that there is an error.
State the extreme test value that shows the error, describe what happens when it is entered, and write a corrected version of the last line.
The value 1 shows the error. When 1 is entered, the condition 1 > 1 is false, so the loop repeats and the user is asked again, although 1 should be accepted.
Corrected line: UNTIL Guests >= 1 AND Guests <= 12
Extreme data tests the smallest and largest acceptable values, here 1 and 12. The value 12 is accepted correctly, but 1 is rejected because the condition uses > instead of >=. This is exactly the kind of error that normal data, such as 6, would never reveal.
1
1 is rejected / the user is asked to enter the number of guests again, even though it should be accepted
UNTIL Guests >= 1 AND Guests <= 12
Accept UNTIL Guests > 0 AND Guests <= 12, or ≥ for >=.
A sports app asks a user to enter the number of minutes they exercised, a whole number from 1 to 90.
Write pseudocode using a REPEAT ... UNTIL loop to input and validate the number of minutes, outputting an error message for any invalid input. Then give the two values of boundary test data for the upper limit and the expected outcome of each.
REPEAT
OUTPUT "Enter minutes of exercise (1 to 90)"
INPUT Minutes
IF Minutes < 1 OR Minutes > 90
THEN
OUTPUT "Invalid: enter a whole number from 1 to 90"
ENDIF
UNTIL Minutes >= 1 AND Minutes <= 90Boundary test data for the upper limit: 90 should be accepted and 91 should be rejected.
The REPEAT ... UNTIL loop keeps asking until the value is in range, and the IF inside gives an error message only for invalid input. The boundary pair for the upper limit is the largest acceptable value (90) and the smallest rejected value (91). Testing both shows the condition uses <= 90 correctly.
MP1 prompts for and inputs the minutes inside a REPEAT ... UNTIL loop
MP2 the loop ends only when Minutes >= 1 AND Minutes <= 90 (or equivalent)
MP3 outputs an error message only when the input is invalid
MP4 90 - accepted
MP5 91 - rejected
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