Running tests by marker (-m) in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pytest run with marker filter

Given the following pytest test file, what tests will run when executing pytest -m "slow"?

PyTest

import pytest

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

@pytest.mark.fast
def test_b():
    assert True

def test_c():
    assert True

A All tests run

B test_a and test_b run

C test_b and test_c run

D Only test_a runs

💡 Hint

The -m option runs tests matching the given marker expression.

The command pytest -m "slow" runs only tests marked with @pytest.mark.slow. Here, only test_a has that marker.

❓ assertion

intermediate

Correct assertion for marker presence in pytest

Which assertion correctly checks that a test function is marked with the marker 'database' in pytest?

PyTest

import pytest

@pytest.mark.database
def test_query():
    pass

A assert any(marker.name == 'database' for marker in test_query.pytestmark)

B assert 'database' in test_query.__pytest_markers__

C assert 'database' in test_query.pytestmark

D assert test_query.has_marker('database')

💡 Hint

pytest stores markers as objects in the pytestmark attribute list.

pytest marks are stored as objects in the list test_query.pytestmark. We must check if any marker's name equals 'database'.

🔧 Debug

advanced

Why does pytest -m 'api and not slow' run no tests?

Given these tests:

import pytest

@pytest.mark.api
@pytest.mark.slow
def test_api_slow():
    pass

@pytest.mark.api
def test_api_fast():
    pass

@pytest.mark.slow
def test_slow():
    pass

Why does pytest -m "api and not slow" run no tests?

A Because the expression excludes all tests marked both api and slow, but test_api_fast is only api so it should run

B Because 'not' is not a valid operator in pytest marker expressions

C Because pytest marker expressions require quotes around 'not'

D Because test_api_fast is not marked slow, so it should run but does not due to syntax error

💡 Hint

Check pytest documentation for valid marker expression operators.

pytest marker expressions support 'and', 'or', but not 'not'. Using 'not' causes no tests to run.

❓ framework

advanced

How to run tests marked 'ui' or 'integration' but not 'slow' in pytest

Which pytest command runs tests marked with 'ui' or 'integration' but excludes those marked 'slow'?

A pytest -m "(ui or integration) and not slow"

B pytest -m "ui or integration and slow"

C pytest -m "ui or integration and not slow"

D pytest -m "ui or integration and not slow" --disable-warnings

💡 Hint

Remember operator precedence and valid operators in pytest marker expressions.

pytest supports 'and' and 'or' but not 'not'. The correct expression is without parentheses and uses 'and' and 'or'.

🧠 Conceptual

expert

Understanding pytest marker expression evaluation order

In pytest marker expressions, which operator has higher precedence?

A 'and' has higher precedence than 'or'

B 'or' has higher precedence than 'and'

C 'and' and 'or' have equal precedence and are evaluated left to right

D Precedence depends on the pytest version and is unpredictable

💡 Hint

Think about how logical operators usually work in programming languages.

In pytest marker expressions, 'and' has higher precedence than 'or', similar to Python logical operators.

Practice

1. What does the -m option do when running pytest?

easy

A. Runs only tests with the specified marker

B. Runs tests in a specific directory

C. Runs tests in parallel

D. Generates a test report

Solution

1. Step 1: Understand pytest markers

   Markers are labels you add to tests to group them logically.

2. Step 2: Use -m option

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

3. Final Answer:

   Runs only tests with the specified marker -> Option A

4. Quick Check:

   pytest -m runs tests by marker = A [OK]

Hint: Remember: -m filters tests by marker name [OK]

Common Mistakes:

• Confusing -m with directory or file options
• Thinking -m runs all tests regardless of marker
• Assuming -m runs tests in parallel

2. Which of the following is the correct syntax to run pytest tests marked as slow?

easy

A. pytest --marker slow

B. pytest -m slow

C. pytest -marker slow

D. pytest --m slow

Solution

1. Step 1: Recall pytest command options

   The correct option to select tests by marker is -m, not --marker or others.

2. Step 2: Match syntax to run tests with marker

   The correct command is pytest -m slow to run tests marked as slow.

3. Final Answer:

   pytest -m slow -> Option B

4. Quick Check:

   Use single dash -m for marker filter = D [OK]

Hint: Use single dash -m, not --marker [OK]

Common Mistakes:

• Using --marker instead of -m
• Adding extra dashes like --m
• Confusing option names

3. Given these tests marked as fast and db:

@pytest.mark.fast
def test_a(): pass

@pytest.mark.db
def test_b(): pass

@pytest.mark.fast
def test_c(): pass

What tests run with the command pytest -m "fast and not db"?

medium

A. test_b only

B. No tests run

C. test_a, test_b, and test_c

D. test_a and test_c

Solution

1. Step 1: Understand the marker expression

   The command runs tests marked with fast AND NOT marked with db.

2. Step 2: Check each test's markers

   test_a and test_c have fast only; test_b has db only.

3. Final Answer:

   test_a and test_c -> Option D

4. Quick Check:

   fast and not db = test_a, test_c [OK]

Hint: Use logical operators to combine markers correctly [OK]

Common Mistakes:

• Including tests marked only with db
• Ignoring the 'not' operator
• Assuming all tests run

4. You run pytest -m slow but no tests run, even though some tests have @pytest.mark.slow. What is the most likely cause?

medium

A. Markers are not registered in pytest.ini

B. You used -m instead of --m

C. The tests are skipped by default

D. The test files are missing

Solution

1. Step 1: Check marker registration

   Pytest requires custom markers to be registered in pytest.ini to avoid warnings and ensure correct filtering.

2. Step 2: Understand effect of missing registration

   If markers are not registered, pytest may ignore them or not run tests filtered by them.

3. Final Answer:

   Markers are not registered in pytest.ini -> Option A

4. Quick Check:

   Unregistered markers cause no tests run = C [OK]

Hint: Always register custom markers in pytest.ini [OK]

Common Mistakes:

• Confusing -m and --m options
• Assuming tests are skipped by default
• Not checking test file presence

5. You have tests marked as api, ui, and db. You want to run tests that are either api or ui, but not db. Which command achieves this?

hard

A. pytest -m "api or (ui and not db)"

B. pytest -m "api or ui and not db"

C. pytest -m "(api or ui) and not db"

D. pytest -m "api and ui and not db"

Solution

1. Step 1: Understand operator precedence

   Logical AND has higher precedence than OR, so parentheses are needed to group api or ui together.

2. Step 2: Analyze each option

   pytest -m "(api or ui) and not db" correctly groups (api or ui) and excludes db with and not db.

3. Final Answer:

   pytest -m "(api or ui) and not db" -> Option C

4. Quick Check:

   Use parentheses to group OR conditions = A [OK]

Hint: Use parentheses to group markers with OR before AND [OK]

Common Mistakes:

• Ignoring operator precedence without parentheses
• Using AND instead of OR between api and ui
• Including db tests by mistake