Code Testing

2.9. Code Testing#

2.9.1. Path Coverage#

It’s important that you’re able to test your code to verify that it will behave the way you intend. An common way to test code is to come up with input-output pairs and check whether your program produces the correct output. We also want to be selective when choosing our input output pairs so that we get path coverage, i.e. our input-output pairs test every possible path in our code.

Example: The purpose of this program is to identify whether x is positive, negative or 0.

x = int(input('x: '))

if x < 0:
    print('x is a negative number')
elif x > 0:
    print('x is a positive number')
else:
    print('x is 0!')

This program has 3 possible paths.

So examples of input-output pairs we can use to test this program so that we get path coverage are:

Input	Expected output
-3	x is a negative number
0	x is 0!
2	x is a positive number

Note that the second column is our expected output. We should run our code to determine whether the code output actually matches our expected output.

2.9.2. Boundary Values#

Another thing we often want to test are boundary values. These are where it causes our program to change. When we have a condition, e.g. x < 3, we should check what happens when x is:

less than 3
exactly 3
greater than 3

And ensure the results are what we expect.

Example

current_speed = int(input("What is your current speed? "))

speed_limit = 40

if current_speed > speed_limit:
    print(
        "You are speeding! {}km/h is above the speed limit of {}km/h. Slow down!".format(
            current_speed, speed_limit
        )
    )
else:
    print("You are travelling within the speed limit.")

In this program we want to test what happens when current_speed is near speed_limit.

If we test 41 (just above 40) our program outputs You are speeding! 41km/h is above the speed limit of 40km/h. Slow down!
At exactly 40 our program outputs You are travelling within the speed limit.
And at 39 (just below 40) our program again outputs You are travelling within the speed limit.

2.9.3. Faulty and Abnormal Data#

Faulty and abnormal data is when the values fall outside the expectations of the system. Whether your not these inputs should be invalid or not will depend on the program specifications, which describes what the code is meant to do (or not meant to do). The program should always be able to handle all valid inputs, but what happens when invalid data is entered is often up to the programmer to decide.

Example

If we look at the same program as in the previous example, invalid, i.e. faulty/abnormal input data would include anything that cannot be converted to an integer. This is because in the first line of the program the user input is converted to an integer.

current_speed = int(input("What is your current speed? "))

Examples of faulty and abnormal data would include hello and 3.5.

Question 1

The following program asks the user what the weather is like. If it’s rainy the program is meant to remind the user to take an umbrella, if it’s sunny the program is meant to remind the user to take a hat and if it’s cold the program is meant to remind the user to take a jumper. The program should always remind the user to take their phone regardless of the weather.

Below is table of input-output pairs.

	Input	Expected output
A	rainy	Take an umbrealla! Don’t forget to take your phone!
B	sunny	Take a hat!! Don’t forget to take your phone!
C	cold	Take a jumper Don’t forget to take your phone!
D	windy	Don’t forgt to take your phone!

Which input-output pairs does the following code fail on?

weather = input("What's the weather like today? ")

if weather == 'rainy':
    print('Take an umbrella!')
    print("Don't forget to take your phone!")

if weather == 'sunny':
    print('Take a hat!')
    print("Don't forget to take your phone!")

if weather == 'cold':
    print('Take a jumper!')

Select all that apply.

Code Testing

Contents

2.9. Code Testing#

2.9.1. Path Coverage#

2.9.2. Boundary Values#

2.9.3. Faulty and Abnormal Data#