Testing a function with assert

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Quick Questions

Shade in the A or B circle for each question.

1. Which line correctly tests that add(2, 3) gives 5?

A assert add(2, 3) = 5

B assert add(2, 3) == 5

2. What happens when an assert condition is False?

A Python raises an AssertionError

B Python prints False and carries on quietly

3. What does Python do when an assert condition is True?

A Nothing, and the program keeps running

B It prints True on the screen

4. Which is the best way to run many test cases on a function?

A Test one case by hand and assume the rest work

B Put the cases in a list and use a for loop with assert

5. A function should return a student's grade from 0 to 100. Which set of inputs is a good test plan?

A A normal mark like 65, boundaries 0 and 100, and an invalid mark like -5

B Only the mark 65, tried three times

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1assert add(2, 3) == 5		AUses = (assignment) instead of == (comparison), which causes a SyntaxError
2for x, want in tests: assert double(x) == want		BRuns the same assert check on every test case in a list
3A boundary test checks a value at the edge of the allowed range, such as 0 or 100		CThe expected value is wrong, because add(2, 3) is 5, so the test fails with an AssertionError
4An invalid input test checks the function handles a bad value like a negative number		Dassert is_pass(50) == True
5assert add(2, 3) = 5		EChecks that add(2, 3) gives 5 and raises an AssertionError if it does not
6assert add(2, 3) == 6		Fassert grade(-5) == "Invalid"

Definitions

assert

Fill in the Blanks

Complete each line of code by filling in the missing parts.

______ add(2, 3) == 5

assert add(2, 3) __ 5

cases = [(1, 2, 3), (0, 0, 0)] for a, b, expected in cases: assert add(a, b) == ________

assert positive(0) == _____

tests = [(2, 3, 5), (0, 0, 0)] ___ a, b, expected in tests: assert add(a, b) == expected

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A def add(a b):

B return a + b

C assert add(2, 3) == 5

Question 2

A def double(n):

B return n * 2

C assert double(4) = 8

Question 3

A def is_even(n):

B return n % 2 == 0

C assert is_even(4) == False

D print("Test passed")

Question 4

A def square(n):

B return n + n

C assert square(3) == 9

D assert square(0) == 0

Question 5

A tests = [(-3, 3), (4, 4), (0, 0)]

B for x, want in tests

C assert abs(x) == want

Answer Key

Testing a function with assert

Section A: Quick Questions

B — assert add(2, 3) == 5

A — Python raises an AssertionError

A — Nothing, and the program keeps running

B — Put the cases in a list and use a for loop with assert

A — A normal mark like 65, boundaries 0 and 100, and an invalid mark like -5

Section B: Match the Pairs

assert add(2, 3) == 5 → Checks that add(2, 3) gives 5 and raises an AssertionError if it does not

for x, want in tests: assert double(x) == want → Runs the same assert check on every test case in a list

A boundary test checks a value at the edge of the allowed range, such as 0 or 100 → assert is_pass(50) == True

An invalid input test checks the function handles a bad value like a negative number → assert grade(-5) == "Invalid"

assert add(2, 3) = 5 → Uses = (assignment) instead of == (comparison), which causes a SyntaxError

assert add(2, 3) == 6 → The expected value is wrong, because add(2, 3) is 5, so the test fails with an AssertionError

Section C: Definitions

assert — Checks a condition is True, like assert add(2, 3) == 5. If the result is not what you expected, it raises an AssertionError, so test cases can run automatically.

Section D: Fill in the Blanks

assert add(2, 3) == 5

cases = [(1, 2, 3), (0, 0, 0)]
for a, b, expected in cases:
    assert add(a, b) == expected

assert positive(0) == False

tests = [(2, 3, 5), (0, 0, 0)]
for a, b, expected in tests:
    assert add(a, b) == expected

Section E: Spot the Error

A — The parameters must be separated by a comma. It should be def add(a, b):

C — A single = assigns a value, so it can't be used to compare. assert needs the comparison operator ==, so it should be assert double(4) == 8

C — 4 is even, so is_even(4) returns True. The expected value is wrong, so assert raises an AssertionError. It should be == True.

B — The function adds instead of multiplying, so square(3) gives 6 and the assert fails. It should be return n * n.

B — A for loop header must end with a colon. It should be for x, want in tests: