Asserting log messages in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this pytest log assertion?

Consider this pytest test function that asserts a log message is emitted at WARNING level.

PyTest

import logging
import pytest

def func():
    logging.warning("Warning issued")

def test_log_warning(caplog):
    with caplog.at_level(logging.WARNING):
        func()
    assert "Warning issued" in caplog.text

A Test fails with AssertionError

B Test passes (assertion succeeds)

C Test raises a RuntimeError

D Test raises a TypeError

💡 Hint

Check if the log message is captured by caplog at the correct level.

The function emits a WARNING log. The test sets caplog to WARNING level and asserts the message is in caplog.text, so the assertion passes.

❓ assertion

intermediate

Which assertion correctly checks for an ERROR log message using caplog?

You want to assert that the log contains the exact message "Error occurred" at ERROR level.

A assert "Error occurred" in caplog.text and caplog.level == logging.ERROR

B assert caplog.text == "Error occurred" and caplog.records[0].level == logging.ERROR

C assert any(record.levelname == "ERROR" and record.getMessage() == "Error occurred" for record in caplog.records)

D assert caplog.records[0].levelname == "ERROR" and caplog.records[0].msg == "Error occurred"

💡 Hint

caplog.records is a list of log records; check each record's levelname and message.

Option C correctly iterates over all records and checks both levelname and message. Others either check only first record or use wrong attributes.

🔧 Debug

advanced

Why does this pytest log assertion fail unexpectedly?

Given this test code: import logging def func(): logging.info("Info message") def test_log_info(caplog): with caplog.at_level(logging.WARNING): func() assert "Info message" in caplog.text Why does the assertion fail?

A Because caplog.text is empty due to a missing caplog fixture

B Because the log message text is incorrect

C Because logging.info does not produce any log output

D Because caplog is set to WARNING level, INFO messages are not captured

💡 Hint

Check the log level filter set by caplog.at_level.

caplog.at_level(logging.WARNING) filters out messages below WARNING, so INFO messages are ignored and not captured.

❓ framework

advanced

Which pytest fixture is used to capture log messages during tests?

You want to capture and assert log messages emitted by your code in pytest tests. Which fixture should you use?

A caplog

B logfixture

C logcap

D logcapture

💡 Hint

The fixture name starts with 'cap'.

pytest provides the 'caplog' fixture to capture log messages during tests.

🧠 Conceptual

expert

What is the main benefit of asserting log messages in automated tests?

Why do testers assert log messages in their automated test suites?

A To verify that the system reports important events and errors as expected

B To increase test execution speed by skipping functional checks

C To replace UI tests with log checks entirely

D To ensure logs are stored permanently on disk

💡 Hint

Think about why logs are useful in software.

Asserting logs helps confirm that the system reports key events and errors, aiding debugging and monitoring.

Practice

1. What is the purpose of the caplog fixture in pytest when testing log messages?

easy

A. To capture log messages generated during test execution

B. To mock external API calls

C. To measure test execution time

D. To generate random test data

Solution

1. Step 1: Understand the role of caplog

   The caplog fixture is designed to capture log messages during pytest test runs.

2. Step 2: Identify correct usage context

   It helps verify that expected log messages are produced, which is essential for testing logging behavior.

3. Final Answer:

   To capture log messages generated during test execution -> Option A

4. Quick Check:

   caplog captures logs [OK]

Hint: Remember: caplog captures logs during tests [OK]

Common Mistakes:

• Confusing caplog with mocking tools
• Thinking caplog measures time
• Assuming caplog generates data

2. Which of the following is the correct way to set the log level to capture WARNING messages but not INFO messages using caplog in pytest?

easy

A. caplog.set_level(logging.INFO)

B. caplog.set_level(logging.ERROR)

C. caplog.set_level(logging.DEBUG)

D. caplog.set_level(logging.WARNING)

Solution

1. Step 1: Understand log levels

   To capture WARNING messages but not INFO, the log level must be set to WARNING.

2. Step 2: Identify correct method call

   Using caplog.set_level(logging.WARNING) sets the capture level to WARNING, capturing WARNING and above.

3. Final Answer:

   caplog.set_level(logging.WARNING) -> Option D

4. Quick Check:

   Set level to WARNING to capture warnings [OK]

Hint: Set caplog level to desired severity (e.g., WARNING) [OK]

Common Mistakes:

• Setting level too high to capture lower severity logs
• Using incorrect logging level constants
• Not calling set_level at all

3. Given the following pytest test code, what will be the result of the assertion?

import logging

def test_log_message(caplog):
    with caplog.at_level(logging.ERROR):
        logging.error('Error occurred')
    assert 'Error occurred' in caplog.text

medium

A. Test passes because the error message is captured

B. Test fails because caplog.text is empty

C. Test fails due to syntax error

D. Test passes but assertion is incorrect

Solution

1. Step 1: Analyze log capture level

   The test sets caplog to capture ERROR level logs, and an error message is logged.

2. Step 2: Check assertion logic

   The assertion checks if the logged message is in caplog.text, which contains all captured logs as text.

3. Final Answer:

   Test passes because the error message is captured -> Option A

4. Quick Check:

   Logged ERROR message found in caplog.text [OK]

Hint: Check caplog.text contains your logged message [OK]

Common Mistakes:

• Assuming caplog.text is empty without setting level
• Confusing caplog.records with caplog.text
• Forgetting to set log level

4. Identify the error in the following pytest test code that uses caplog to assert a log message:

import logging

def test_info_log(caplog):
    logging.info('Info issued')
    assert 'Info issued' in caplog.text

medium

A. Logging function used is wrong

B. Incorrect assertion syntax

C. Missing setting log level to capture INFO messages

D. caplog fixture is not imported

Solution

1. Step 1: Check log level setting

   The test logs an INFO but does not set caplog to capture INFO level logs, so no logs are captured.

2. Step 2: Understand impact on assertion

   Because no logs are captured, caplog.text is empty and the assertion fails.

3. Final Answer:

   Missing setting log level to capture INFO messages -> Option C

4. Quick Check:

   Set caplog level to INFO before logging [OK]

Hint: Always set caplog level before logging messages [OK]

Common Mistakes:

• Not using caplog.at_level or caplog.set_level
• Assuming logs are captured by default
• Incorrectly placing assertion before logging

5. You want to test that your function logs an INFO message containing the word 'success'. Which pytest caplog assertion correctly verifies this?

hard

A. assert caplog.records.count('success') == 1

B. assert any('success' in record.message for record in caplog.records if record.levelname == 'INFO')

C. assert caplog.text == 'success'

D. assert 'success' in caplog.records[0]

Solution

1. Step 1: Understand caplog.records structure

   caplog.records is a list of log record objects with attributes like message and levelname.

2. Step 2: Choose correct assertion logic

   assert any('success' in record.message for record in caplog.records if record.levelname == 'INFO') checks if any INFO level record contains 'success' in its message, which correctly verifies the log content.

3. Final Answer:

   assert any('success' in record.message for record in caplog.records if record.levelname == 'INFO') -> Option B

4. Quick Check:

   Use caplog.records with message and levelname for assertions [OK]

Hint: Use caplog.records with message and levelname for checks [OK]

Common Mistakes:

• Using count on records list incorrectly
• Comparing caplog.text directly to a string
• Accessing caplog.records elements as strings