Pytest Test Framework¶

Pytest is a powerful and flexible testing framework for Python. It simplifies writing and running tests, making it an essential tool for ensuring code quality.

Installation¶

To install Pytest, use uv:

uv pip install pytest

Basic Usage¶

  1. Create Test Files:

    • Tests are typically placed in a tests/ directory.

    • Test file names should start with test_ or end with _test.py.

    • Test functions should start with test_.

  2. Write Tests:

    • Use assert statements to verify expected behavior.

    # tests/test_example.py
def add(a, b):
    return a + b

def test_add():
    assert add(2, 3) == 5
    assert add(-1, 1) == 0
    assert add(0, 0) == 0

  3. Run Tests:

    • Navigate to the project root directory.

    • Run uvx pytest or just pytest if your virtual environment is activated.

    uvx pytest

Key Features¶

  • Simple Assertions: Use standard assert statements for test conditions.

  • Test Discovery: Automatically finds test files and functions.

  • Fixtures: Define reusable test components.

  • Parametrization: Run the same test with multiple inputs.

  • Plugins: Extend functionality with a wide range of plugins.

Configuration¶

Pytest can be configured using a pytest.ini, pyproject.toml, or tox.ini file. Here’s an example pyproject.toml configuration:

# pyproject.toml
[tool.pytest.ini_options]
testpaths = ["tests"]
python_files = ["test_*.py"]

  • testpaths: Specifies the directories to search for tests.

  • python_files: Specifies the file naming pattern for test files.

Fixtures¶

Fixtures are functions that provide a fixed baseline for tests. They are used to set up and tear down resources, such as database connections or temporary files.

import pytest

@pytest.fixture
def temp_file(tmp_path):
    file = tmp_path / "tempfile.txt"
    file.write_text("Hello, Pytest!")
    return file

def test_file_content(temp_file):
    assert temp_file.read_text() == "Hello, Pytest!"

Best Practices¶

  • Keep Tests Isolated: Each test should be independent and not rely on the state of other tests.

  • Use Descriptive Names: Test function names should clearly describe what is being tested.

  • Test Edge Cases: Include tests for boundary conditions and error handling.

  • Use Fixtures Wisely: Use fixtures to reduce code duplication and improve test readability.

  • Follow the Arrange-Act-Assert Pattern:

    • Arrange: Set up the test environment and prepare the inputs.

    • Act: Execute the code being tested.

    • Assert: Verify the expected results.

Troubleshooting¶

  • Tests Not Being Discovered:

    • Ensure test files and functions follow the naming conventions.

    • Check the testpaths and python_files settings in pyproject.toml.

  • Import Errors:

    • Make sure your project is installed in editable mode (uv pip install --editable .).

    • Verify that your virtual environment is activated.

By following these guidelines, you can effectively use Pytest to write and run tests, ensuring the reliability and quality of your Python code.