Marker registration in PyTest - Build an Automation Script

Verify pytest marker registration and usage

Preconditions (2)

Step 1: Create a test file test_sample.py

Step 2: Add a test function test_example marked with @pytest.mark.smoke

Step 3: Run pytest with the -m smoke option to select tests with the smoke marker

✅ Expected Result: Only the test_example function runs and passes without marker warnings

Automation Requirements - pytest

Assertions Needed:

Verify test_example runs when using -m smoke

Verify no warnings about unregistered markers appear

Best Practices:

Register custom markers in pytest.ini

Use @pytest.mark.<marker_name> decorator

Use pytest command line option -m to select tests by marker

Avoid hardcoding marker names in test code

Automated Solution

PyTest

import subprocess
import sys
import pytest

# pytest.ini content to register marker
pytest_ini_content = """
[pytest]
markers =
    smoke: mark a test as smoke test
"""

# Write pytest.ini file
with open('pytest.ini', 'w') as f:
    f.write(pytest_ini_content)

# test_sample.py content
test_code = '''
import pytest

@pytest.mark.smoke

def test_example():
    assert True
'''

with open('test_sample.py', 'w') as f:
    f.write(test_code)

# Run pytest with -m smoke
result = subprocess.run([sys.executable, '-m', 'pytest', '-m', 'smoke', '--tb=short', '-q'], capture_output=True, text=True)

# Check output for test run and no warnings
assert 'test_example' in result.stdout, 'test_example did not run'
assert 'WARNING' not in result.stdout, 'Found warnings about markers'
assert result.returncode == 0, f'Pytest failed with code {result.returncode}'

print('Test passed: marker registration and usage works correctly')

This script automates the verification of pytest marker registration.

First, it creates a pytest.ini file registering the smoke marker to avoid warnings.

Then it writes a test file test_sample.py with a test function marked with @pytest.mark.smoke.

It runs pytest with the -m smoke option to select only tests with the smoke marker.

Assertions check that the test ran, no warnings about markers appeared, and pytest exited successfully.

This approach ensures the marker is properly registered and used, following best practices.

Common Mistakes - 4 Pitfalls

Not registering custom markers in pytest.ini

Using marker names inconsistently or misspelling them

Hardcoding marker names in test code without registration

Running pytest without the -m option to select markers

Bonus Challenge

Now add data-driven testing with 3 different test functions each marked with different custom markers registered in pytest.ini

Show Hint

Practice

1. What is the main purpose of registering markers in pytest.ini?

easy

A. To avoid warnings when using custom markers in tests

B. To automatically run all tests without specifying markers

C. To disable all markers in the test suite

D. To change the default test discovery pattern

Solution

1. Step 1: Understand marker registration role

   Markers must be registered in pytest.ini to inform pytest about custom markers.

2. Step 2: Identify effect of registration

   Without registration, pytest shows warnings about unknown markers; registration prevents these warnings.

3. Final Answer:

   To avoid warnings when using custom markers in tests -> Option A

4. Quick Check:

   Marker registration = avoid warnings [OK]

Hint: Register markers in pytest.ini to stop warnings [OK]

Common Mistakes:

• Thinking registration runs tests automatically
• Believing registration disables markers
• Confusing marker registration with test discovery

2. Which of the following is the correct syntax to register a custom marker named slow in pytest.ini?

easy

A. [pytest]
markers = slow: marks tests as slow

B. [markers]
slow = marks tests as slow

C. [pytest]
marker = slow: marks tests as slow

D. [pytest]
markers = slow marks tests as slow

Solution

1. Step 1: Recall pytest.ini marker syntax

   Markers are registered under the [pytest] section with the key 'markers' followed by marker descriptions.

2. Step 2: Match correct syntax

   [pytest] markers = slow: marks tests as slow correctly uses '[pytest]' section and 'markers = slow: marks tests as slow' format.

3. Final Answer:

   [pytest] markers = slow: marks tests as slow -> Option A

4. Quick Check:

   Correct section and key = [pytest] markers = slow: marks tests as slow [OK]

Hint: Use [pytest] and 'markers =' to register markers [OK]

Common Mistakes:

• Using wrong section name like [markers]
• Misspelling 'markers' key
• Omitting colon after marker name

3. Given the following pytest.ini content and test code, what will be the result when running pytest -m slow?

[pytest]
markers = slow: marks tests as slow

import pytest

@pytest.mark.slow
def test_example():
    assert True

def test_fast():
    assert True

medium

A. Only test_fast runs and passes

B. Both test_example and test_fast run and pass

C. Only test_example runs and passes

D. No tests run due to marker misconfiguration

Solution

1. Step 1: Understand -m slow option

   The -m slow option runs only tests marked with @pytest.mark.slow.

2. Step 2: Identify marked tests

   test_example is marked with @pytest.mark.slow, test_fast is not.

3. Final Answer:

   Only test_example runs and passes -> Option C

4. Quick Check:

   Run with -m slow = only slow tests run [OK]

Hint: -m runs only tests with matching marker [OK]

Common Mistakes:

• Assuming all tests run with -m option
• Confusing marker name with test function name
• Ignoring marker registration effect

4. You added a custom marker database to your tests but pytest shows a warning: PytestUnknownMarkWarning. What is the most likely cause and how to fix it?

medium

A. You must run pytest with --disable-warnings to hide the message

B. You forgot to register the database marker in pytest.ini; add it under [pytest] markers

C. You need to rename the marker to db to avoid warnings

D. You used @pytest.mark.database incorrectly; remove the decorator

Solution

1. Step 1: Identify cause of PytestUnknownMarkWarning

   This warning appears when a custom marker is used but not registered in pytest.ini.

2. Step 2: Fix by registering marker

   Add database marker under the [pytest] section in pytest.ini to register it and remove the warning.

3. Final Answer:

   You forgot to register the database marker in pytest.ini; add it under [pytest] markers -> Option B

4. Quick Check:

   Warning = missing marker registration [OK]

Hint: Register all custom markers in pytest.ini to avoid warnings [OK]

Common Mistakes:

• Ignoring the warning and continuing
• Removing marker decorator instead of registering
• Trying to rename marker instead of registering

5. You want to run tests marked as api but skip those marked as slow. Your pytest.ini contains:

[pytest]
markers =
    api: marks API tests
    slow: marks slow tests

Which command correctly runs only api tests excluding slow tests?

hard

A. pytest -m "not api and slow"

B. pytest -m "api or slow"

C. pytest -m "slow and not api"

D. pytest -m "api and not slow"

Solution

1. Step 1: Understand marker expressions with -m

   The -m option accepts boolean expressions combining markers using and, or, and not.

2. Step 2: Build expression for api tests excluding slow

   We want tests marked api but not slow, so expression is api and not slow.

3. Final Answer:

   pytest -m "api and not slow" -> Option D

4. Quick Check:

   Run api tests excluding slow = pytest -m "api and not slow" [OK]

Hint: Use -m "api and not slow" to include/exclude markers [OK]

Common Mistakes:

• Using 'or' instead of 'and not' excludes wrong tests
• Misplacing 'not' operator
• Confusing marker names in expression