Asserting warnings (pytest.warns) - Test Execution Trace

Test Overview

This test checks if a specific warning is raised during the execution of a function. It verifies that the warning message matches the expected text.

Test Code - pytest

PyTest

import warnings
import pytest

def deprecated_function():
    warnings.warn("This function is deprecated", DeprecationWarning)

def test_deprecated_warning():
    with pytest.warns(DeprecationWarning) as record:
        deprecated_function()
    assert len(record) == 1
    assert str(record[0].message) == "This function is deprecated"

Execution Trace - 7 Steps

Step	Action	System State	Assertion	Result
1	Test starts	pytest test runner is ready	-	PASS
2	Calls test_deprecated_warning function	Inside test function context	-	PASS
3	Enters pytest.warns context manager expecting DeprecationWarning	Warning capture context active	-	PASS
4	Calls deprecated_function which triggers DeprecationWarning	Warning emitted and captured in record	Warning of type DeprecationWarning is captured	PASS
5	Exits pytest.warns context manager	Captured warnings stored in record	record contains exactly one warning	PASS
6	Asserts warning message text matches expected string	Warning message is 'This function is deprecated'	Warning message equals 'This function is deprecated'	PASS
7	Test ends successfully	All assertions passed	-	PASS

Failure Scenario

Failing Condition: No DeprecationWarning is raised by deprecated_function

Execution Trace Quiz - 3 Questions

What does pytest.warns check in this test?

A That no warnings are raised

B That the function returns a specific value

C That a DeprecationWarning is raised during the function call

D That the function raises an exception

Key Result

Use pytest.warns to catch and verify warnings in your code. This helps ensure your code warns users correctly and your tests confirm the warning details.