Marker registration in PyTest

Introduction

Markers help you label tests so you can run or skip groups easily.

You want to run only slow tests separately from fast ones.

You want to skip tests that need a database when it's not available.

You want to mark tests that check a new feature under development.

You want to group tests by priority or type for better organization.

Syntax

PyTest

[pytest]
markers =
    marker_name: description of the marker

# In test file
import pytest

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

Markers must be registered in pytest.ini to avoid warnings.

Use @pytest.mark.marker_name above test functions to apply markers.

Examples

This example registers a slow marker and uses it on a test.

PyTest

[pytest]
markers =
    slow: marks tests as slow

# test_sample.py
import pytest

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

This example shows a database marker for tests needing a database.

PyTest

[pytest]
markers =
    database: marks tests that need database

# test_db.py
import pytest

@pytest.mark.database
def test_db_connection():
    assert True

Sample Program

This test file has two tests marked with smoke and one without any marker.

You can run only smoke tests with pytest -m smoke.

PyTest

# pytest.ini
[pytest]
markers =
    smoke: quick tests to check basic features

# test_smoke.py
import pytest

@pytest.mark.smoke
def test_basic_feature():
    assert 1 + 1 == 2

@pytest.mark.smoke
def test_another_basic():
    assert 'a'.upper() == 'A'


def test_not_marked():
    assert True

Important Notes

Always register markers in pytest.ini to keep tests clean and avoid warnings.

You can combine markers with and, or, and not when running tests.

Markers help organize tests and make running specific groups easy and fast.

Summary

Markers label tests for easy grouping and running.

Register markers in pytest.ini to avoid warnings.

Use @pytest.mark.marker_name above test functions to apply markers.

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