A lift with a button

You press a lift button. The lift comes. You do not know how the lift works inside.

A lift engineer can open the panel and look at the inside. That person tests in a different way.

We test software in both ways: from outside, and from inside.

Key words

Word	What it means	Example
Closed box testing	Testing with no view of the code. We only give inputs and check outputs.	Press Buy and see the receipt
Open box testing	Testing with the code in view. Also called structural testing.	Test every if and else
Structural testing	Another name for open box testing: it follows the structure of the code.	Test every path
Path	One route through the code.	The code inside one if
Automatic testing	A program runs the tests for you.	Run 500 checks in a minute
Manual testing	A person runs the tests by hand.	Press each button
AI tool	A program that can write text or code when you ask it.	A chat assistant
Requirement	Something the product must do.	Users can log in
Function	A named piece of code that does one job.	grade(score)
Unit test	A test of one small part, such as one function.	Test the grade function
Test case	One input and the answer we expect.	Input 3, expect 6

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Closed box and open box

	Closed box	Open box
What the tester sees	Only inputs and outputs	The code inside
Who often does it	Testers, users, the client	The developer
How tests are chosen	From the requirements	From the paths in the code
Example	Type 45 and check the grade says near	See the line if score >= 40 and make sure a test reaches it
Weak point	Cannot see code that is never reached	Can miss a requirement the code forgot

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Try it: find the paths

Code: python

def grade(score):
    if score < 0 or score > 100:
        return "invalid"
    if score >= 50:
        return "pass"
    if score >= 40:
        return "near"
    return "fail"

for score in [75, 45, 10, 150]:
    print(score, grade(score))

# There are 4 paths. Did the four scores above reach all of them?
# (>= means "is bigger than or equal to")

Open box finds the limits

data-callouts.tip.label

In the code, >= means "is bigger than or equal to". So score >= 50 means 50 or more. Test 49, 50 and 51. Mistakes often hide where an if changes the answer.

Manual and automatic testing

Manual testing: a person runs the test. Good for new things, how a page feels and odd ideas.

Automatic testing: a program runs the tests. Good for tests you repeat, such as after every change. A computer does not get bored and does not forget a step.

Using AI tools to help

An AI tool can help you test. You can ask it for test ideas, for odd inputs, or to write the first version of unit tests.

It is fast. But it can be wrong, and it does not know your requirements. You must read and run what it writes.

Using an AI tool: ask, read, run, add

Step	What you do	Example
Ask	Type a clear prompt (the words you give the AI)	Write 5 test cases for grade(score). 50 or more is a pass. Scores go from 0 to 100.
Read	Check each test against the rule	Is the expected answer right for 50?
Run	Run every test. Fix any test that is wrong	The AI wrote 49 as a pass. That is wrong.
Add	Add the tests the AI missed	Add -1 and 101, which are not allowed.

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Rules for AI help

data-callouts.warning.label

Check every test the AI writes. Do not paste passwords or private data into it. You are responsible for the result, not the AI.