snapshottest

A hands-on demo for inline-snapshot — the pytest plugin that writes your expected values for you.

Just run ./demo.sh and see the full workflow in action: create snapshots from live API calls, break them with a new feature, and fix them in one command. No slides, no reading — one script, real understanding.

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What is this?

A small Python CLI that fetches your location (via ip-api.com) and current weather (via Open-Meteo), then displays a report.

The interesting part is the tests: they hit the real APIs, and --inline-snapshot=create writes the expected values into the test file automatically.

An interactive demo walks you through the full workflow in three acts:

1. Create — fill empty snapshots from live API responses
2. Break — add a feature (continent) that changes the data shape
3. Fix — update all snapshots in one command

Tip: Read the full step-by-step walkthrough in TUTORIAL.md.

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Requirements

• Python 3.11+
• UV — a fast Python package manager
• Internet connection (the tests call live APIs)

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Install UV

If you don't have UV yet, install it with a single command:

curl -LsSf https://astral.sh/uv/install.sh | sh

Note: On macOS you can also use brew install uv. See the UV docs for other options.

Verify it works:

$ uv --version
uv 0.6.x

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Clone & install

git clone https://github.com/miguelp/snapshottest.git
cd snapshottest
uv sync

That's it. uv sync creates the virtual environment and installs all dependencies.

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Run the demo

./demo.sh

The script is idempotent — run it as many times as you want. It resets everything on each run and restores files on exit.

It will:

1. Write a test file with empty snapshot() calls
2. Run --inline-snapshot=create to fill them from live APIs
3. Apply the continent feature (breaks existing snapshots)
4. Run --inline-snapshot=create,fix to update everything in one pass

Info: The demo requires an internet connection. It calls ip-api.com and Open-Meteo — both free, no API key needed.

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Run the CLI

uv run python -m snapshottest.cli weather

Or as JSON:

uv run python -m snapshottest.cli weather --json

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Run the tests

uv run pytest tests/ -v

To fill empty snapshots:

uv run pytest tests/ -v --inline-snapshot=create

Tip: See all available flags in the inline-snapshot docs.

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Project structure

snapshottest/
├── src/snapshottest/
│   ├── models.py            # Location, Weather, WeatherReport
│   ├── location.py          # IP geolocation (ip-api.com)
│   ├── weather.py           # Current weather (Open-Meteo)
│   └── cli.py               # Typer CLI + Rich output
├── tests/
│   ├── conftest.py          # Network guard (skip when offline)
│   ├── test_demo.py         # Real-API tests with inline snapshots
│   └── test_weather_report.py  # Error-path test
├── demo/
│   └── continent/           # Feature files used by demo.sh
├── demo.sh                  # Interactive 3-act demo
├── TUTORIAL.md              # Full written tutorial
└── pyproject.toml

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Learn more

• TUTORIAL.md — step-by-step guide through the whole workflow
• inline-snapshot docs — the library this demo is built around
• UV docs — the package manager used here