caplog for log messages in PyTest - Test Execution Trace

Test Overview

This test checks if a function logs the expected messages using pytest's caplog fixture. It verifies that the log contains a specific info message.

Test Code - pytest

PyTest

import logging
import pytest

logging.basicConfig(level=logging.INFO)

def greet(name):
    logging.info(f"Greeting {name}")
    return f"Hello, {name}!"


def test_greet_logs(caplog):
    with caplog.at_level(logging.INFO):
        result = greet("Alice")
    assert result == "Hello, Alice!"
    assert "Greeting Alice" in caplog.text

Execution Trace - 6 Steps

Step	Action	System State	Assertion	Result
1	Test starts	pytest test runner initialized	-	PASS
2	Function greet("Alice") is called inside caplog context at INFO level	Logging system captures INFO messages	-	PASS
3	greet logs message: 'Greeting Alice'	Log record with message 'Greeting Alice' stored in caplog	-	PASS
4	Function greet returns 'Hello, Alice!'	Return value captured in variable result	assert result == 'Hello, Alice!'	PASS
5	Check if 'Greeting Alice' is in captured logs	caplog.text contains logged messages	assert 'Greeting Alice' in caplog.text	PASS
6	Test ends	All assertions passed	-	PASS

Failure Scenario

Failing Condition: The function does not log the expected message or logs at a different level

Execution Trace Quiz - 3 Questions

What does the caplog fixture capture during the test?

A Return values of functions

B Exceptions raised in the test

C Log messages emitted during the test

D Test execution time

Key Result

Use caplog to verify that your code logs important messages correctly. This helps catch issues early by checking logs during tests.