Assert with messages in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ assertion

intermediate

Understanding assert messages in pytest

What will be the output message when this pytest assertion fails?

PyTest

def test_sum():
    result = 2 + 2
    assert result == 5, "Sum calculation failed! Expected 5 but got {result}"

A AssertionError: Sum calculation failed! Expected 5 but got {result}

B No error, test passes

C AssertionError: Sum calculation failed! Expected 5 but got 5

D AssertionError: Sum calculation failed! Expected 5 but got 4

💡 Hint

Check how the assert message string is formatted.

The assert message is a plain string and does not use f-string formatting, so {result} is not replaced by its value.

❓ assertion

intermediate

Correct use of assert message with variable interpolation

Which option correctly shows how to include the variable 'result' in the assert message so it displays its value?

PyTest

def test_multiply():
    result = 3 * 3
    assert result == 10, ???

A f"Multiplication failed! Expected 10 but got {result}"

B "Multiplication failed! Expected 10 but got {result}"

C "Multiplication failed! Expected 10 but got " + result

D "Multiplication failed! Expected 10 but got %d" % result

💡 Hint

Use Python f-strings for variable interpolation inside strings.

Only option A uses an f-string, which correctly replaces {result} with its value 9.

❓ Predict Output

advanced

Output of pytest assertion with message

What is the output when running this pytest test?

PyTest

def test_divide():
    value = 10 / 2
    assert value == 6, f"Division result incorrect: got {value}"

A AssertionError: Division result incorrect: got 5.0

B Test passes with no output

C TypeError: unsupported operand type(s) for /: 'int' and 'str'

D AssertionError: Division result incorrect: got 6

💡 Hint

Check the actual value of value and the assertion condition.

value is 5.0, not 6, so assertion fails and message shows the actual value 5.0.

🔧 Debug

advanced

Debugging assert message with wrong formatting

Why does this pytest assertion raise a SyntaxError?

PyTest

def test_subtract():
    result = 10 - 3
    assert result == 8, f"Subtraction failed: got {result"

A Variable 'result' is undefined causing NameError

B Missing closing brace '}' in the f-string causes SyntaxError

C Assertion condition is false causing AssertionError

D No error, test passes

💡 Hint

Check the f-string syntax carefully.

The f-string is missing a closing brace '}', so Python raises SyntaxError before running the test.

❓ framework

expert

Best practice for assert messages in pytest

Which option is the best practice for writing assert messages in pytest to help debugging when tests fail?

A Use plain strings without variable values to keep messages short

B Avoid assert messages; rely on pytest default output only

C Use detailed f-string messages showing expected and actual values

D Write assert messages only for passing tests

💡 Hint

Think about what helps you understand test failures quickly.

Detailed messages with actual and expected values help quickly identify what went wrong.