Custom markers in PyTest - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a custom marker in pytest?

A custom marker is a label you create to tag tests for special handling, like grouping or skipping them during test runs.

beginner

How do you define a custom marker in pytest?

You define a custom marker by adding it to the pytest.ini file under the [pytest] section using the markers option.

beginner

How do you apply a custom marker to a test function?

Use the @pytest.mark.<marker_name> decorator above the test function to apply the custom marker.

beginner

What command runs only tests with a specific custom marker?

Use pytest -m '<marker_name>' to run only tests tagged with that custom marker.

intermediate

Why should you register custom markers in pytest.ini?

Registering markers avoids warnings and helps pytest recognize your custom tags properly.

How do you mark a test with a custom marker named 'slow'?

A @pytest.mark.slow

B @slow

C mark('slow')

D pytest.mark('slow')

Use the decorator @pytest.mark.slow to apply the 'slow' marker to a test.

Where do you register custom markers to avoid warnings?

A test file header

B conftest.py

C setup.py

D pytest.ini

Custom markers should be registered in pytest.ini under the [pytest] section.

What does the command 'pytest -m slow' do?

A Skips tests marked with 'slow'

B Runs only tests marked with 'slow'

C Runs all tests except those marked 'slow'

D Runs tests with names containing 'slow'

The -m option runs only tests that have the specified marker.

What happens if you use a custom marker without registering it?

A Tests run but marker is ignored silently

B Tests fail to run

C Pytest shows a warning about unknown markers

D Pytest crashes

Pytest warns about unknown markers if they are not registered.

Which file is best for defining markers used across many test files?

A pytest.ini

B test_example.py

C requirements.txt

D README.md

pytest.ini is the central place to register markers for all tests.

Explain how to create and use a custom marker in pytest.

Think about registration, tagging, and running tests.

Why is it important to register custom markers in pytest.ini?

Consider what happens if you don't register.

Practice

1. What is the main purpose of using custom markers in pytest?

easy

A. To generate test data automatically

B. To change the Python interpreter version

C. To automatically fix test failures

D. To label tests for grouping and selective running

Solution

1. Step 1: Understand what custom markers do

   Custom markers in pytest are used to tag tests with labels for easier management.

2. Step 2: Identify the purpose of these labels

   These labels help run specific groups of tests selectively using the marker name.

3. Final Answer:

   To label tests for grouping and selective running -> Option D

4. Quick Check:

   Custom markers = test grouping [OK]

Hint: Markers tag tests to run groups easily [OK]

Common Mistakes:

• Thinking markers change Python version
• Assuming markers fix test errors automatically
• Confusing markers with test data generation

2. Which of the following is the correct syntax to mark a test with a custom marker named slow?

easy

A. @pytest.mark.slow\ndef test_example(): pass

B. @pytest.slow.mark\ndef test_example(): pass

C. @pytest.mark[slow]\ndef test_example(): pass

D. @pytest.mark('slow')\ndef test_example(): pass

Solution

1. Step 1: Recall pytest marker syntax

   Custom markers use dot notation: @pytest.mark.markername before the test function.

2. Step 2: Match the correct syntax

   @pytest.mark.slow is the correct way to apply the 'slow' marker.

3. Final Answer:

   @pytest.mark.slow\ndef test_example(): pass -> Option A

4. Quick Check:

   Marker syntax = @pytest.mark.name [OK]

Hint: Use dot notation: @pytest.mark.name [OK]

Common Mistakes:

• Using parentheses instead of dot notation
• Using square brackets instead of dot notation
• Placing marker after function name

3. Given the following test file, what will be the output when running pytest -m slow?

import pytest

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

def test_b():
    assert True

@pytest.mark.slow
def test_c():
    assert False

medium

A. Runs all tests; test_c fails

B. Runs only test_b; all pass

C. Runs test_a and test_c; test_c fails, test_a passes

D. Runs test_a and test_b; all pass

Solution

1. Step 1: Understand what pytest -m slow does

   This command runs only tests marked with the 'slow' marker.

2. Step 2: Identify marked tests in the code

   test_a and test_c have @pytest.mark.slow, so only these run.

3. Step 3: Check test results

   test_a passes (assert True), test_c fails (assert False).

4. Final Answer:

   Runs test_a and test_c; test_c fails, test_a passes -> Option C

5. Quick Check:

   pytest -m slow runs marked tests only [OK]

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

Common Mistakes:

• Assuming all tests run with -m option
• Ignoring test failures in marked tests
• Running unmarked tests by mistake

4. What is wrong with this pytest marker usage?

import pytest

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

medium

A. Markers should not have parentheses unless parameters are used

B. Marker name must be uppercase

C. The test function must have parameters

D. pytest.mark cannot be used on test functions

Solution

1. Step 1: Check marker syntax

   Markers without parameters should not have parentheses; @pytest.mark.slow() is incorrect.

2. Step 2: Correct usage

   Use @pytest.mark.slow without parentheses for simple markers.

3. Final Answer:

   Markers should not have parentheses unless parameters are used -> Option A

4. Quick Check:

   Use parentheses only with marker args [OK]

Hint: No parentheses for simple markers [OK]

Common Mistakes:

• Adding empty parentheses to markers
• Using uppercase marker names incorrectly
• Thinking markers require function parameters

5. You want to run tests marked as database but exclude those also marked as slow. Which pytest command achieves this?

hard

A. pytest -m "database or slow"

B. pytest -m "database and not slow"

C. pytest -m "not database and slow"

D. pytest -m "database and slow"

Solution

1. Step 1: Understand marker expressions

   pytest supports boolean expressions with markers: and, or, not.

2. Step 2: Formulate the correct expression

   To run tests marked 'database' but exclude 'slow', use "database and not slow".

3. Final Answer:

   pytest -m "database and not slow" -> Option B

4. Quick Check:

   Use boolean logic in -m to include/exclude markers [OK]

Hint: Use boolean logic: -m "marker and not other" [OK]

Common Mistakes:

• Using 'or' instead of 'and not' to exclude
• Misplacing 'not' before the first marker
• Combining markers without quotes