snaptestv2 1.0.0

Snapshot testing for Python — auto-create, diff on mismatch, pytest plugin, and CLI

snaptest

Snapshot testing for Python — automatically creates snapshots on first run, shows clear diffs on mismatch, pytest plugin included, and a CLI to manage snapshots. Zero dependencies.

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Installation

pip install snaptest

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Quick Start

# pytest style
def test_api_response(snap):
    result = get_users()
    snap(result)   # creates snapshot on first run, asserts on next runs

# Update snapshots when output intentionally changes
pytest --snapshot-update
# or
SNAPTEST_UPDATE=1 pytest

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Usage

pytest Fixture

def test_user_list(snap):
    users = api.get_users()
    snap(users)

def test_multiple_snapshots(snap):
    snap(api.get_users(),   key="users_list")
    snap(api.get_profile(), key="user_profile")

Standalone (without pytest)

from snaptest import snapshot

def test_output():
    result = transform_data(raw_input)
    snapshot(result)              # auto-named from function + line number
    snapshot(result, key="data")  # named snapshot

Updating Snapshots

# Via pytest flag
pytest --snapshot-update

# Via environment variable
SNAPTEST_UPDATE=1 pytest

# Programmatically
from snaptest import update_snapshot
update_snapshot(new_value, key="my_snapshot")

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Snapshot Files

Snapshots are stored as human-readable text files next to your test files:

tests/
├── test_api.py
├── test_transform.py
└── __snapshots__/
    ├── test_api.snap
    └── test_transform.snap

Commit __snapshots__/ to version control so diffs are visible in PRs.

Snapshot file format

# snaptest snapshot file
# Do not edit manually

[test_user_list_1]
{
  "id": 1,
  "name": "Alice"
}
[/test_user_list_1]

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Diff Output on Mismatch

When a snapshot doesn't match, you get a clear diff:

SnapshotMismatch: 'test_user_list_1'
Snapshot file: tests/__snapshots__/test_api.snap

─── Diff (- expected, + actual) ───────────────────────
--- expected (stored)
+++ actual (current)
@@ -1,5 +1,5 @@
 {
   "id": 1,
-  "name": "Alice",
+  "name": "Alice Smith",
   "active": true
 }
────────────────────────────────────────────────────────

To update: SNAPTEST_UPDATE=1 pytest

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Supported Types

Type	How it's stored
dict	JSON with sorted keys
list, tuple	JSON array
set, frozenset	Sorted JSON array
str, int, float, bool, None	JSON scalar
dataclass	JSON via dataclasses.asdict
Any object with __dict__	JSON via vars()
Anything else	repr()

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CLI

# List all snapshot files and keys
snaptest list

# Show a stored snapshot value
snaptest show my_snapshot_key

# Instructions to update
snaptest update

# Delete all snapshot files (with confirmation)
snaptest clean
snaptest clean --yes   # skip confirmation

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API Reference

snapshot(value, key=None, update=False)

Assert value matches stored snapshot. Creates on first run.

update_snapshot(value, key=None)

Force-update a snapshot.

snap fixture (pytest)

def test_something(snap):
    snap(value)              # auto-named
    snap(value, key="name")  # named

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Running Tests

pip install pytest
pytest tests/ -v

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License

MIT © prabhay759