Testing that invalid input is rejected

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. Which line tests that a validator rejects the bad age -5?

A assert is_valid(-5)

B assert not is_valid(-5)

2. True or false: a test for invalid input passes when the validator accepts the bad value.

A False

B True

3. A function should raise a ValueError for a negative age. Which structure checks this?

A if/else only

B try/except ValueError

4. Test: try: check_age(-5) then except ValueError: print('PASS'). What should happen if check_age(-5) raises NO error?

A The test fails, because the expected error never happened

B The test passes, because nothing went wrong

5. Which test data is best for testing that a validator for ages 0 to 120 rejects bad input?

A -5 and 121

B 18 and 65

Match the Pairs

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

Left column		Right column
1assert not is_valid(-5)		Atry: check_age(-5) print("FAIL") except ValueError: print("PASS")
2except ValueError: print("PASS")		Bassert not is_valid(-5)
3To test that a validator rejects a bad value, call it with that value and assert it returns False		CPasses only if is_valid(-5) returns False, so the bad value -5 is correctly rejected
4If bad input should raise an error, put the call in a try block and print PASS in the except block		DThere is no FAIL message after the call in try. If no error occurs, the test never reports a failure, so a broken validator would go unnoticed.
5assert is_valid(-5)		EThis asserts that the bad value is accepted. It should be assert not is_valid(-5), so the test passes only when -5 is rejected.
6try: check_age(-5) except ValueError: print("PASS")		FRuns when the bad input raises a ValueError, which is the expected error, so the test passes

Definitions

assert not is_valid(-5)

Fill in the Blanks

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

assert ___ is_valid(-5)

______ not is_valid(-5)

try: register(-5) except __________:

assert validate(-5) == _____

try: ________(-5) except ValueError:

Spot the Error

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

Question 1

A def is_valid(age):

B return 0 >= age <= 120

C assert not is_valid(-5)

Question 2

A def is_valid(age):

B return 0 <= age <= 120

C assert is_valid(25)

D assert is_valid(-5)

Question 3

A try:

B check_age(-5)

C print("FAIL")

D except TypeError:

E print("PASS")

Question 4

A def test_negative():

B assert not is_valid(5)

C test_negative()

Question 5

A def is_valid(pw)

B return len(pw) >= 8

C assert not is_valid("abc")

Answer Key

Testing that invalid input is rejected

Section A: Quick Questions

B — assert not is_valid(-5)

A — False

B — try/except ValueError

A — The test fails, because the expected error never happened

A — -5 and 121

Section B: Match the Pairs

assert not is_valid(-5) → Passes only if is_valid(-5) returns False, so the bad value -5 is correctly rejected

except ValueError: print("PASS") → Runs when the bad input raises a ValueError, which is the expected error, so the test passes

To test that a validator rejects a bad value, call it with that value and assert it returns False → assert not is_valid(-5)

If bad input should raise an error, put the call in a try block and print PASS in the except block → try: check_age(-5) print("FAIL") except ValueError: print("PASS")

assert is_valid(-5) → This asserts that the bad value is accepted. It should be assert not is_valid(-5), so the test passes only when -5 is rejected.

try: check_age(-5) except ValueError: print("PASS") → There is no FAIL message after the call in try. If no error occurs, the test never reports a failure, so a broken validator would go unnoticed.

Section C: Definitions

assert not is_valid(-5) — Tests that bad input is rejected: call the validator with an invalid value and assert it returns False. If an error is expected, use try/except; no error means the test fails.

Section D: Fill in the Blanks

assert not is_valid(-5)

try:
    register(-5)
except ValueError:

assert validate(-5) == False

try:
    register(-5)
except ValueError:

Section E: Spot the Error

B — The first comparison is the wrong way round. 0 >= age accepts negative numbers, so is_valid(-5) returns True and the assert fails. It should be 0 <= age <= 120.

D — The test expects an invalid value to be accepted. To check that bad input is rejected, it must be assert not is_valid(-5).

D — The test is looking for the wrong error type. The validation code should raise a ValueError, so the line must be except ValueError:.

B — 5 is a valid value, so this does not test invalid input. The test needs a bad value such as -5.

A — The def line is missing its colon at the end. It should be def is_valid(pw): or Python raises a SyntaxError.