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Testing & modern typing

pytest basics, mocks, type hints, TypedDict, Protocol, and static-checking patterns.

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Testing & modern typing medium

How to Snapshot Test JSON with Mock in Python

Use pytest-snapshot to capture the exact output of a JSON-loading function, with and without mocking json.loads, so future changes are automatically detected.

pytest snapshot mock
Python 
import json
from unittest.mock import Mock, patch
import pytest


def load_config(data):
    config = json.loads(data)
    return {"host": config["host"], "port": config["port"]}


def test_load_config_snapshot(snapshot):
    mock_data = json.dumps({"host": "localhost", "port": 8080, "extra": "ignored"})
    result = …
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