Running tests by marker (-m) in PyTest - Build an Automation Script

Run pytest tests filtered by marker

Preconditions (2)

Step 1: Open terminal or command prompt

Step 2: Navigate to the directory containing the test file

Step 3: Run pytest with the -m option to specify the marker 'smoke'

Step 4: Observe that only tests marked with @pytest.mark.smoke are executed

✅ Expected Result: Only tests with the 'smoke' marker run and pass or fail accordingly

Automation Requirements - pytest

Assertions Needed:

Verify that only tests with the specified marker run

Verify that tests without the marker do not run

Best Practices:

Use @pytest.mark.<marker_name> to mark tests

Use pytest command line option -m '<marker_name>' to filter tests

Keep test markers meaningful and documented

Automated Solution

PyTest

import pytest

@pytest.mark.smoke
 def test_smoke_1():
     assert 1 + 1 == 2

@pytest.mark.smoke
 def test_smoke_2():
     assert 'a' * 3 == 'aaa'

@pytest.mark.regression
 def test_regression_1():
     assert 5 > 2

@pytest.mark.regression
 def test_regression_2():
     assert len([1, 2, 3]) == 3

# To run only smoke tests, execute in terminal:
# pytest -m smoke

# Expected output: only test_smoke_1 and test_smoke_2 run

The code defines four test functions with two different markers: smoke and regression.

Using @pytest.mark.smoke marks tests as smoke tests, and @pytest.mark.regression marks others as regression tests.

Running pytest -m smoke in the terminal runs only the tests marked with smoke. This filters tests by marker, so tests without the marker are skipped.

This approach helps run specific groups of tests quickly, like smoke tests for basic checks.

Common Mistakes - 3 Pitfalls

{'mistake': 'Not marking tests with @pytest.mark before running with -m', 'why_bad': "The -m option filters by markers, so if tests are not marked, they won't be selected.", 'correct_approach': 'Always decorate tests with @pytest.mark.<marker_name> before using -m to filter.'}

Using incorrect marker name in the -m option

Hardcoding test names instead of using markers for filtering

Bonus Challenge

Add a new marker 'fast' and create two tests with it. Run tests filtered by 'fast' marker.

Show Hint

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