Marker registration in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Purpose of marker registration in pytest

Why is it important to register custom markers in pytest's pytest.ini or pyproject.toml file?

A To avoid warnings about unknown markers during test runs and enable marker-based test selection.

B To automatically generate test reports without additional plugins.

C To speed up test execution by caching marker results.

D To disable all tests that use custom markers by default.

💡 Hint

Think about what happens if pytest sees a marker it does not recognize.

Registering markers tells pytest about custom labels you use on tests. Without registration, pytest shows warnings and may not allow selecting tests by those markers.

❓ Predict Output

intermediate

Output of pytest when using unregistered marker

What output will pytest produce when running this test with an unregistered marker @pytest.mark.slow?

PyTest

import pytest

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

A Skips the test silently without any warning.

B Fails the test immediately with a SyntaxError.

C Runs the test without any warning or message.

D Runs the test and shows a warning: 'PytestUnknownMarkWarning: Unknown pytest.mark.slow - is this a typo?'.

💡 Hint

Think about pytest's behavior when it sees a marker it does not know.

Pytest runs the test but warns about unknown markers to alert you to possible typos or missing registrations.

❓ locator

advanced

Correct location to register a custom marker

Where should you add the registration for a custom marker named integration to avoid warnings in pytest?

A In the test function's docstring describing the test purpose.

B Directly inside each test file as a comment above the test function.

C In the <code>pytest.ini</code> file under the <code>[pytest]</code> section with <code>markers = integration: marks tests as integration tests</code>.

D In the <code>setup.py</code> file as an entry point for pytest.

💡 Hint

Think about pytest configuration files that control test behavior globally.

The pytest.ini file is the standard place to register markers so pytest knows about them project-wide.

❓ assertion

advanced

Assertion to verify marker presence on a test function

Given a test function decorated with @pytest.mark.api, which assertion correctly checks for the presence of the 'api' marker in a pytest hook?

PyTest

def pytest_collection_modifyitems(items):
    for item in items:
        # Which assertion is correct here?
        pass

A assert 'api' in item.keywords

B assert any(mark.name == 'api' for mark in item.iter_markers())

C assert item.marker == 'api'

D assert item.has_marker('api')

💡 Hint

Look at how pytest exposes markers on collected test items.

The iter_markers() method returns all markers on a test item. Checking their names is the correct way.

❓ framework

expert

Effect of missing marker registration on test selection

You have registered a custom marker db in pytest.ini. You run pytest -m db to select tests with this marker. What happens if you remove the marker registration but still run pytest -m db?

A Pytest runs only tests with the <code>db</code> marker but shows a warning about unknown marker.

B Pytest runs all tests ignoring the <code>-m db</code> option silently.

C Pytest raises an error and stops because the marker is unknown and cannot be used for selection.

D Pytest skips all tests because no tests match the unregistered marker.

💡 Hint

Consider pytest's behavior when selecting tests by an unregistered marker.

Pytest allows selection by unregistered markers but warns about unknown markers. It runs only matching tests.

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