Pytest Markers

• Markers are decorators (@pytest.mark.<markername>) applied to tests to attach metadata.
• Built-in markers like skip, skipif, xfail, and parametrize provide predefined behaviors.
• Custom markers (e.g., slow, integration, api) help categorize tests by project-specific criteria.
• Applying markers allows Pytest (and plugins) to filter, select, or modify tests during collection and execution.

Skipping Tests Unconditionally: @pytest.mark.skip

• The skip marker unconditionally prevents a test from running, useful when a feature is disabled or under refactor.
• Skipped tests show an s in the summary along with the provided reason.
• Use @pytest.mark.skip(reason="...") to disable tests without removing their code.

Skipping Tests Conditionally: @pytest.mark.skipif

• The skipif marker skips tests only when a specified condition evaluates to true at collection time.
• Conditions can be expressions like sys.platform != "linux" or checks for optional dependencies.
• This enables platform-specific, version-specific, or resource-dependent test filtering.

Expected Failures: @pytest.mark.xfail

• The xfail marker marks tests expected to fail due to known bugs or unimplemented features.
• Expected failures are reported as XFAIL and don’t cause the suite to fail; unexpected passes are reported as XPASS.

Custom Markers and Registration

• Custom markers (e.g., slow, api, integration) help organize and categorize tests by functionality or runtime.
• Tests can have multiple markers for fine-grained control (e.g., @pytest.mark.api and @pytest.mark.integration).
• To avoid warnings, register custom markers in pytest.ini or pyproject.toml under the markers option.

Running Tests by Marker (m option)

• The -m <expression> CLI option selects tests matching a marker expression.
• Expressions support logical operators: and, or, and negation with not.
• Examples: pytest -m slow, pytest -m "not slow", pytest -m "api and integration".

Common Pitfalls & How to Avoid Them

• Overusing skip hides failures; prefer xfail for known bugs to maintain visibility.
• Complex skipif conditions reduce readability; delegate logic to helper functions when needed.
• Typos in marker names create unregistered markers; register all custom markers to catch errors early.
• Forgetting to register markers leads to warnings; always define marker descriptions in configuration files.

import pytest
import time

try:
    import some_optional_library  # type: ignore
except ModuleNotFoundError:
    some_optional_library = None
# Section: Skipping Tests Unconditionally: @pytest.mark.skip

@pytest.mark.skip(
    reason="Skipping experimental feature until completion."
)
def test_new_experimental_feature() -> None:
    assert False

# Section: Skipping Tests Conditionally: @pytest.mark.skipif

@pytest.mark.skipif(
    some_optional_library is None,
    reason="Requires 'some_optional_library' to be installed.",
)
def test_with_optional_dependency() -> None:
    print(
        f"Running tests that depends on an optional library..."
    )
    assert some_optional_library

# Section: Expected Failures: @pytest.mark.xfail

@pytest.mark.xfail(
    reason="Bug #123: Division by zero not handled properly."
)
def test_divide_by_zero() -> None:
    _division = 1 / 0
    assert False

@pytest.mark.xfail  # Add strict=True to make XPASS lead to a failure
def test_expected_to_fail() -> None:
    assert True

# Section: Custom Markers and Registration

@pytest.mark.slow
def test_very_long_computations() -> None:
    time.sleep(5)
    assert True

@pytest.mark.api
@pytest.mark.smoke
def test_user_creation() -> None:
    assert True

# Section: Running Tests by Marker (m option)