approvaltests

What it is and what it does

ApprovalTests is a snapshot-based testing library that compares test output against previously approved golden-master files. Instead of writing brittle assertions for complex objects, you capture the actual output, review it in a diff tool, and approve it as the expected result. On subsequent runs, any deviation from the approved output triggers a diff comparison, letting you decide whether the change is intentional or a regression.

The library integrates with pytest and unittest, supports CLI invocation for cross-language testing, and includes reporters that launch external diff tools (like your system's native diff viewer or IDE integrations). It handles long strings, large arrays, HTML, and structured objects—scenarios where line-by-line assertion code becomes unwieldy. Extra dependencies unlock optional features like clipboard reporting, HTML verification, and pairwise test combination.

Use it for:

• Verify multi-line text output or formatted reports without writing fragile string comparisons.
• Test complex nested data structures (dicts, lists, objects) by comparing their serialized form to an approved snapshot.
• Review HTML generation or template output using a visual diff tool instead of regex assertions.
• Detect unintended changes in API responses or large JSON structures across test runs.
• Manage test data for exercises, katas, or green-field projects using the starter project template.

Worth the install?

AI-flagged interpretation of the facts on this page — verify before relying

ApprovalTests provides a snapshot-based assertion library for testing complex outputs—long strings, large arrays, structured objects—by comparing results against golden-master files and launching diff tools to review changes.

Yes. ApprovalTests fills a genuine gap in Python testing: snapshot-based verification for outputs too complex for simple assertions. Active maintenance, low install friction, permissive license, no known vulnerabilities, and broad Python version support (3.10–3.14) make it a solid choice. Install it if you regularly test long strings, structured objects, or generated content where a diff tool beats manual assertion logic.

Install

approvaltests on PyPI

pip install approvaltests

uv add approvaltests

poetry add approvaltests

Installing approvaltests

Before you install

Low install friction: pure Python wheel with no compiled dependencies. Active maintenance—last commit 2026-08-10, released 2026-08-02. Requires Python 3.10 or later; tested on 3.10, 3.11, 3.12, 3.13, 3.14.

License in practice

Apache-2.0 (permissive): you may use, modify, and distribute this package freely in commercial and open-source projects, provided you include a copy of the license and state any material changes.

Quickstart

pip install approvaltests

from approvaltests.approvals import verify

def test_simple():
    result = "Hello ApprovalTests"
    verify(result)

Requires pytest or unittest as your test runner; reporters (diff tools) are optional but recommended for viewing approval failures.

Verify before relying

• Whether the 10 runtime dependencies (pytest, beautifulsoup4, pyperclip, etc.) are all required or only needed for specific features.
• Performance characteristics when verifying very large objects or arrays.

Package facts

Evidence: approvaltests-19.1.1-py3-none-any.whl

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