Asserting log messages in PyTest - Test Execution Trace

Test Overview

This test checks if a specific log message is generated during the execution of a function. It verifies that the log contains the expected text at the correct log level.

Test Code - pytest

PyTest

import logging
import pytest

logger = logging.getLogger(__name__)

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


def test_greet_logs_info(caplog):
    with caplog.at_level(logging.INFO):
        result = greet("Alice")
    assert result == "Hello, Alice!"
    assert "Greeting Alice" in caplog.text
    assert any(record.levelname == "INFO" for record in caplog.records)

Execution Trace - 7 Steps

Step	Action	System State	Assertion	Result
1	Test starts	pytest test runner is ready	-	PASS
2	Calls greet("Alice") inside caplog context at INFO level	Logger is set to capture INFO messages	-	PASS
3	greet function logs message "Greeting Alice" at INFO level	Log record created with message and INFO level	-	PASS
4	greet returns "Hello, Alice!"	Function output available	Check result equals "Hello, Alice!"	PASS
5	Assert log text contains "Greeting Alice"	caplog.text contains captured logs	Verify "Greeting Alice" in caplog.text	PASS
6	Assert at least one log record has level INFO	caplog.records list available	Check any record.levelname == "INFO"	PASS
7	Test ends successfully	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 test verify about the log messages?

A That the log contains the message "Greeting Alice" at INFO level

B That the log contains any message at DEBUG level

C That no log messages are generated

D That the log contains the message "Hello, Alice!"

Key Result

Always capture and assert log messages explicitly in tests to verify that important events are logged correctly, improving observability and debugging.