Asserting warnings (pytest.warns) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pytest.warns context usage

What will be the output of this pytest test when run?

PyTest

import warnings
import pytest

def test_warning_capture():
    with pytest.warns(DeprecationWarning) as record:
        warnings.warn("Deprecated feature", DeprecationWarning)
    return len(record)

result = test_warning_capture()

A 1

B 0

C Raises AssertionError

D Raises TypeError

💡 Hint

Count how many warnings are captured inside the context.

The pytest.warns context captures warnings of the specified type. Since one DeprecationWarning is issued, the record contains one warning, so len(record) is 1.

❓ assertion

intermediate

Correct assertion to check warning message

Which assertion correctly verifies that the warning message contains the word 'deprecated'?

PyTest

import warnings
import pytest

def test_warning_message():
    with pytest.warns(UserWarning) as record:
        warnings.warn("This feature is deprecated", UserWarning)
    warning_message = str(record[0].message)
    # Which assertion below is correct?

A assert warning_message == 'deprecated'

B assert 'deprecated' in warning_message

C assert warning_message.startswith('deprecated')

D assert warning_message is 'deprecated'

💡 Hint

Check if the substring is anywhere in the message.

The warning message is 'This feature is deprecated', so checking if 'deprecated' is contained anywhere is correct. Exact equality or startswith will fail.

🔧 Debug

advanced

Identify the error in warning assertion

What error will this test raise when run?

PyTest

import warnings
import pytest

def test_wrong_warning():
    with pytest.warns(DeprecationWarning):
        warnings.warn("Use new API", UserWarning)

A AssertionError

B No error, test passes

C TypeError

D RuntimeWarning

💡 Hint

Check if the warning type matches the expected one.

The test expects a DeprecationWarning but the code issues a UserWarning. pytest.warns raises AssertionError if the expected warning is not raised.

❓ framework

advanced

Using pytest.warns as a function decorator

Which option correctly uses pytest.warns as a decorator to check for a warning?

PyTest

import warnings
import pytest

# Choose the correct decorator usage

A

@pytest.warns(DeprecationWarning)
def test_func():
    pass

B

@pytest.mark.warns(DeprecationWarning)
def test_func():
    warnings.warn("Deprecated", DeprecationWarning)

C

@pytest.warns(UserWarning)
def test_func():
    warnings.warn("Deprecated", DeprecationWarning)

D

@pytest.warns(DeprecationWarning)
def test_func():
    warnings.warn("Deprecated", DeprecationWarning)

💡 Hint

Check the correct decorator name and matching warning type.

pytest.warns can be used as a decorator to check that the decorated function raises the specified warning. Option D correctly uses it with matching warning type.

🧠 Conceptual

expert

Behavior of pytest.warns with multiple warnings

If a code block inside pytest.warns(WarningType) emits multiple warnings, how does pytest.warns behave?

A It only passes if exactly one warning of WarningType is raised

B It fails if more than one warning is raised, even if all are WarningType

C It passes if at least one warning of WarningType is raised, ignoring others

D It raises an error if any warning other than WarningType is raised

💡 Hint

Think about how pytest.warns matches warnings inside the block.

pytest.warns passes if at least one warning of the expected type is raised. It does not fail if multiple warnings occur, nor does it fail for other warnings unless they cause test failure separately.