Registry / testing / pytest-regressions

pytest-regressions

library2.11.0pypypi✓ verified 24d ago

pytest-regressions is a Pytest plugin that provides a set of fixtures to simplify writing regression tests. It helps in maintaining tests that generate substantial or specific data files, such as dictionaries, dataframes, images, or numeric tables. The plugin stores expected data as baselines in a data directory (leveraging pytest-datadir) and compares future test runs against these baselines, providing detailed diffs upon failure. The current version is 2.10.0, and it maintains a regular release cadence with frequent minor updates.

testing

pip install pytest-regressions

github ↗package ↗

INSTALL

IMPORT

SIG · PYTEST-REGRESSIONS

pytest-regressions

testingpythonv2.11.0

Install

2.9s avg

Import

—

Disk

33MB

Pass rate

10/ 10

Env Coverage10 / 10

glibc

3.9–3.13

musl

3.9–3.13

Install & Compatibility

Where this runs

tested against v2.11.0 · pip install

no network on importno background threads

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

py 3.10–3.95 runs

installs and imports cleanly · install 0.0s · import 0.000s · 33.5MB

glibc

py 3.10–3.95 runs

installs and imports cleanly · install 2.9s · import 0.000s · 35MB

33MB installed

● package 33MB

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

data_regression

✓ def test_data(data_regression): # No explicit import needed, pytest discovers fixtures automatically

pytest-regressions fixtures (e.g., `data_regression`, `file_regression`, `image_regression`) are automatically discovered by pytest. You do not need explicit `import` statements; just declare the fixture as an argument in your test function.

This quickstart demonstrates using the `data_regression` fixture to test a dictionary output. The first run with this test will generate a `test_grids_data.yml` file in the automatically created `data` directory (or a custom one if configured). Subsequent runs will compare the output of `summary_grids()` against the contents of this YAML file. If they differ, the test fails with a detailed diff.

import pytest def summary_grids(): # In a real scenario, this would compute/read values return { "Main Grid": { "id": 0, "cell_count": 1000, "active_cells": 300, "properties": [ {"name": "Temperature", "min": 75, "max": 85}, {"name": "Porosity", "min": 0.3, "max": 0.4}, ], }, } def test_grids_data(data_regression): data = summary_grids() data_regression.check(data)

Debug

Known issues

gotchaUsing the `--force-regen` or `--regen-all` pytest flags will regenerate and overwrite existing baseline files without failing the tests. While useful for updating baselines, misuse can lead to unintentional data loss if not carefully managed and committed to version control.

fix

Only use `--force-regen` or `--regen-all` when intentionally updating baselines. Always review the changes to the generated files before committing them to version control.

affects: All versions

gotchaSpecific regression fixtures like `dataframe_regression`, `image_regression`, `num_regression`, and `ndarrays_regression` rely on optional dependencies (pandas, Pillow, numpy) which are NOT installed automatically with `pip install pytest-regressions`. Attempting to use these fixtures without the respective dependencies will result in `ImportError` or similar issues.

fix

Install the required optional dependencies manually, e.g., `pip install pytest-regressions[dataframe]` or `pip install pandas Pillow numpy` depending on the fixtures you intend to use.

affects: All versions

gotchaWhen using parametrized tests with regression fixtures, a separate regression file will be generated for each parameterization. This can lead to a large number of baseline files and potentially very long filenames if parameter names are extensive, which might exceed operating system path length limits.

fix

Be mindful of parameter naming in parametrized tests to keep filenames concise. Consider using custom `basename` arguments for fixtures if default naming creates issues, or overriding `pytest-datadir` fixtures for more controlled path generation.

affects: All versions

Upgrade

Version history

2.11.0latest on PyPI · released May 25, 2026

Audit

Dependencies

pytestrequiredCore testing framework that the plugin extends.

pytest-datadirrequiredManages the data directory for storing and retrieving regression baselines.

PyYAMLrequiredUsed for serialization/deserialization of YAML files by the data_regression fixture.

pandasoptionalRequired for the dataframe_regression fixture to handle pandas DataFrames.

PillowoptionalRequired for the image_regression fixture to handle image comparisons.

numpyoptionalRequired for the num_regression and ndarrays_regression fixtures to handle numeric data and arrays.

Agent activity

15 hits · last 30 days

node

Resources

githubhttps://github.com/ESSS/pytest-regressions ↗

packagehttps://pypi.org/project/pytest-regressions/ ↗