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Syrupy - Pytest Snapshot Testing

Syrupy is a zero-dependency pytest snapshot testing plugin that enables asserting the immutability of computed results through simple, idiomatic assertions.

Docs: https://syrupy-project.github.io/syrupy/

What is Syrupy?

Syrupy is a snapshot testing library that:

• Captures the output/state of code at a point in time
• Compares future test runs against saved snapshots
• Automatically manages snapshot files in __snapshots__ directories
• Integrates naturally with pytest's assertion syntax

Core Philosophy

Three Design Principles:

1. Extensible: Easy to add support for custom/unsupported data types
2. Idiomatic: Natural pytest-style assertions (assert x == snapshot)
3. Sound: Fails tests if snapshots are missing or different

Target Use Case: Testing complex data structures, API responses, UI components, or any computed results that should remain stable over time.

Snapshot Fixture API

Core Methods

The snapshot fixture accepts several options per assertion:

• matcher: Control how objects are serialized
• exclude: Filter out properties from snapshots
• include: Include only specific properties
• extension_class: Use a different serialization format
• diff: Capture only differences from a base
• name: Custom name for the snapshot

Usage with Options

assert data == snapshot(matcher=my_matcher, exclude=my_filter, name="custom_name")

Built-in Extensions

Syrupy provides several snapshot extensions for different use cases:

AmberSnapshotExtension (Default)

• Human-readable format
• Stores all snapshots in .ambr files
• Supports all Python built-in types
• Custom object representation via __repr__

JSONSnapshotExtension

• Stores snapshots as JSON files (.json extension)
• Useful for API responses and complex data structures
• Machine-readable format
• Import from syrupy.extensions.json

Usage Example:

import pytest
from syrupy.extensions.json import JSONSnapshotExtension


@pytest.fixture
def snapshot_json(snapshot):
    return snapshot.use_extension(JSONSnapshotExtension)


def test_api_call(client, snapshot_json):
    resp = client.post("/endpoint")
    assert resp.status_code == 200
    assert snapshot_json == resp.json()