Validation, verification and test data

Computer Science · Algorithm design and problem-solving. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

Validation is an automatic check by the program that data is reasonable and follows the rules before it is accepted. It cannot tell whether the data is correct: an age typed as 43 in place of 34 still passes a range check.

Verification checks that data has been entered or copied without change. It compares what was entered with the original. The two methods are a visual check and a double entry check.

Test data is chosen to show that a program works. A good test uses data the program should accept, data it should reject, and data at the limits of what is allowed.

Rules to remember

Range check: the value is between two limits. Length check: the number of characters is correct. Type check: the data is of the right data type.
Presence check: the field has not been left empty. Format check: the characters follow a pattern, such as two letters then four digits.
Check digit: an extra digit calculated from the other digits, used to find errors in a code number such as a barcode.
Visual check: a person compares the data on screen with the source document. Double entry: the data is typed twice and the computer compares the two entries.
Normal data: sensible data the program should accept and process. Abnormal data: data that should be rejected.
Extreme data: the largest and smallest values that are accepted.
Boundary data: the pair of values at each limit, one that is accepted and one that is rejected.

Common mistake

Students mix up extreme and boundary data. Extreme values are both accepted; a boundary pair has one accepted value and one rejected value.

Worked example

A program accepts a student's age as a whole number from 11 to 18 inclusive. Give normal, abnormal, extreme and boundary test data.

Normal: any value well inside the range, for example 14, which should be accepted.
Abnormal: a value that should be rejected, for example 25 or the word 'twelve'.
Extreme: the smallest and largest accepted values, which are 11 and 18.
Boundary: 10 and 11 at the lower limit, 18 and 19 at the upper limit. 10 and 19 are rejected.

Answer: Normal 14; abnormal 25; extreme 11 and 18; boundary 10 with 11, and 18 with 19.

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