2.3 Defensive Design and Testin

Question 1

Data type check

Answer 1

Checks that the value entered is of the required data type
An age has been input as an integer, e.g. 21

Question 2

Range check

Answer 2

Checks that the data is between an upper limit and a lower limit
A probability is between 0 and 1

Question 3

Limit check

Answer 3

Used to check either the upper limit or the lower limit
The price of an item is not below the lower limit of 0.00

Question 4

Length check

Answer 4

Checks that a specific number of characters or digits has been entered
A passport number is exactly 9 digits long

Question 5

Format check

Answer 5

Used to check that the data is in a specified format. Regular expressions can be useful here to match a string against a pattern.
A date is in the format DD/MM/YYYY

Question 6

Presence check

Answer 6

Checks that something has been entered into a field and the field has not been left blank
A ‘City’ field has not been left blank when a user is entering an address

Question 7

Existence check

Answer 7

Used to check that a piece of data or the name of a file actually exists
The surname “Lau” exists in a customer record. The file name “highscores.csv” exists during file handling

Question 8

Consistency check

Answer 8

Checks that pieces of data from two or more fields are compatible with each other
The number entered for the day of the month is not higher than 29 if the month chosen is February

Question 8

Uniqueness check

Answer 8

Checks that a value entered is a new and original value
A username has not already been chosen when a user is creating a new account

Question 9

Check digit

Answer 9

A digit that helps confirm that a code is correct
The last digit of a barcode is calculated from all of the numbers before it

Question 10

Data Type

Answer 10

E.g. string, integer, character, float, Boolean. An attribute of a data item that determines the values that can be stored and the operations that can be carried out on the data item.

Question 11

Casting

Answer 11

Changing the data type of a piece of data, for example converting a string to an integer

Question 12

String

Answer 12

A sequence of characters, e.g. letters, numbers, spaces and other symbols

Question 13

Integer

Answer 13

A whole number that is either positive or negative. Examples: 5, 14, -29

Question 14

Float

Answer 14

A data type for a number with a decimal place. Stored as a floating point number.

Question 15

Function

Answer 15

A named block of code that performs a task and returns one or more values

Question 16

Syntax

Answer 16

The precise way that program statements must be written to be understood by the computer. It is specific to the programming language in use.

Question 17

Syntax error

Answer 17

When the translator does not recognise the keywords or commands entered. Common errors of this type include mistyping a keyword or missing out brackets.

Question 18

Logic error

Answer 18

When code runs correctly but the program does not work as expected or produce the expected output.

Question 19

Runtime error

Answer 19

When an error occurs during the use of the program. Common errors of this type include trying to divide by zero or accessing an item in an array that does not exist.

Question 20

Testing

Answer 20

The systematic process of checking that a subroutine, program, or system works as expected

Question 21

Test data

Answer 21

Data that has been carefully selected for testing. It should include normal, boundary and erroneous values as appropriate

Question 22

Boundary data

Answer 22

Test data that is on the limit of the acceptable range of valid data

Question 23

Erroneous data

Answer 23

Test data that should be caught by validation and rejected by a system