A-level Computing/AQA/Paper 1/Systematic approach to problem solving/Testing





Once we have created our solution we need to test that the whole system functions effectively. To do this should be easy, as all we need to do is compare the finished product next to the objectives that we set out in the Analysis. There are several ways of testing a system, you need to know them all and the types of data that might be used.

Test Plan
At an early stage in a project you should consider how the system will be tested to see if it works correctly. There are three main test methodologies that you need to be aware of, and able to choose between.

Black Box Testing
Consider the box to contain the program source code, you don't have access to it and you don't have to be aware of how it works. All you do is input data and test to see if the output is as expected. The internal workings are unknown, they are in a black box. Examples of Black Box testing would be if you were working as a games tester for a new console game. You wouldn't have been involved in the design or coding of the system, and all you will be asked to do is to input commands to see if the desired results are output.

White Box Testing
With white box testing you understand the coding structure that makes up the program. All the tests that you perform will exercise the different routes through the program, checking to see that the correct results are output.

Dry Run Testing
A dry run is a mental run of a computer program, where the computer programmer examines the source code one step at a time and determines what it will do when run. In theoretical computer science, a dry run is a mental run of an algorithm, sometimes expressed in pseudocode, where the computer scientist examines the algorithm's procedures one step at a time. In both uses, the dry run is frequently assisted by a trace table. And whilst we are here we might as well get some more practice in:

Complete the trace table for the following code:

Complete the trace table for the following code:

Summary
Name the suitable testing methods for each of the following scenarios:


 * You don't have access to the source code and need to check that some input produces the desired output:

Black Box Testing as you don't have access to the internal workings of the program


 * There is a bug somewhere in the code producing the wrong output for a given input, you have access to the code

Dry Run Testing as you have access to the source and this will allow you to find the offending line(s) of programming

Dry run test the following algorithms:

Typical, Erroneous, Extreme
There are three types of test data we can use. What are they? The answer lies mostly in their name, let's take a look at this example where someone has created a secondary school registration system which lets students register themselves. We don't want people who are too young attending, and we don't want students who are too old. In fact we are looking for students 11–16 years old.
 * A Typical Student will be 12,13,14 or 15
 * An Erroneous (or wrong) aged student will be 45, 6 or any age outside those allowed.
 * An Extreme (or boundary) aged student has just started or is just about to leave, they will be 11 or 16

If you are testing data that has Typical, Erroneous and Extreme data, show tests for all three. Some tests might only have typical and erroneous, for example entering a correct password might only have a typical and an erroneous value. Some things might only have typical testing, such as if a button to a next page works or not, or if a calculation is correct.

Imagine that the following objectives were set:

The maximum number of yellow cards a player can receive in a game is 2

Typical : 0,1,2 (most likely to list 1)

Erroneous: 3, -6

Extreme: 0,2

There should be no more than 15 minutes extra time in a game

Typical : 0,1m45,9m23

Erroneous: -6, 15m01

Extreme: 0,15m00

The name of a team should be no longer than 20 characters

Typical : Monster United

Erroneous: Monster and Dagrington League of Gentlefolk

Extreme: Moincicestier United (20 characters!)

List the typical, erroneous and extreme data for the following:

Typical : 5,16,18
 * The number of cigarettes currently in a 20 cigarette carton:

Erroneous: 21, -7

Extreme: 0 or 20

Typical : 28,56,32
 * The age of a college teacher:

Erroneous: 16, 86

Extreme: 21, 68

Typical : GH24
 * The username for a system that must be of the form   :

Erroneous: G678

Extreme: AA00, ZZ99

Typical : 12/07/1987
 * The date for someone's birthday:

Erroneous: 31/09/1987, 31/02/1987

Extreme: 31/12/1999, 01/01/2001 (this is harder to specify, it might depend on the age range you allow)


 * Someone's hair colour:

Typical : brown, red, black

Erroneous: bicycle

Extreme: n/a (we're not here to judge people!)

Typical : 28
 * Does the following calculation work: 14 * 2

Erroneous: n/a

Extreme: n/a


 * Number of pages in a book

Typical : 24, 500

Erroneous: -9

Extreme: 1 (notice no upper end, this is assuming that it wouldn't be a book without any pages!)


 * Name a date in February:

Typical : 23th, 16th

Erroneous: 30th (you might also mention leap years here)

Extreme: 1st, 28th or 29th (depending on leap years)