Configuring Pytest

• As you start using Pytest extensively, typing -v or -m on the command line every time becomes tedious.
• Centralize your defaults in pyproject.toml under the [tool.pytest.ini_options] table.
• A single source of truth means every developer—and your CI system—runs tests with the same settings.
• Putting Pytest alongside other PEP 518 tools (Black, isort, Flake8) keeps your repo tidy and consistent.

Why a Configuration File?

• Consistency: Run pytest without remembering flags; everyone gets the same behavior.
• Simplicity: Remove boilerplate from docs and CI scripts.
• Project-specific discovery: Set testpaths, python_files and markers in one place.
• Cleaner output: Declare markers to silence PytestUnknownMarkWarning, enable color and rich tracebacks by default.

Configuration File Hierarchy

Pytest searches for settings in this order, using the first match from the current or a parent directory:

1. pyproject.toml under [tool.pytest.ini_options]
2. pytest.ini
3. tox.ini with a [pytest] section
4. setup.cfg under [tool:pytest]

Embrace pyproject.toml as the modern hub for all your tool configurations.

Creating pyproject.toml

1. Create or open pyproject.toml at your project root.
2. Add a [tool.pytest.ini_options] table.
3. Define your defaults using TOML syntax and inline strings.

Common Configuration Options

• addopts
  Defines default command-line flags that Pytest applies on every run (verbosity, reporting, color, etc.).

• markers
  Pre-registers custom markers with descriptions so that you can categorize tests and avoid unknown-marker warnings.

• testpaths
  Restricts test discovery to the listed directories, preventing Pytest from scanning other parts of the project.

• python_files
  Specifies filename patterns that Pytest treats as test files (e.g., test_*.py).

• python_classes
  Indicates class name patterns Pytest will consider when looking for test classes (e.g., classes starting with Test).

• python_functions
  Sets function name patterns Pytest uses to identify individual test functions (e.g., functions beginning with test_).

• Other options

  • norecursedirs: directories to skip during discovery
  • minversion: enforce a minimum Pytest version
  • filterwarnings: configure how warnings are handled
  • and many more built-in settings for fine-tuning

Example of pyproject.toml

from typing import TypedDict
import re

class TextAttributes(TypedDict):
    word_count: int
    unique_words: set[str]
    average_word_length: float
    longest_word: str

def calculate_text_attributes(input_text: str) -> TextAttributes:
    split_text = re.findall(r"\w+", input_text)
    word_length_sum = sum(len(word) for word in split_text)
    avg_word_length = (
        word_length_sum / len(split_text)
        if len(split_text)
        else 0
    )

    return {
        "word_count": len(split_text),
        "unique_words": set(text.lower() for text in split_text),
        "average_word_length": avg_word_length,
        "longest_word": (
            max(split_text, key=len) if split_text else ""
        ),
    }