How to Mock Environment Variables in Python

import os

class EnvInjector:
    def __init__(self, mock_vars=None):
        self.mock_vars = mock_vars or {}
        self.original = {}

    def __enter__(self):
        for key, value in self.mock_vars.items():
            if key in os.environ:
                self.original[key] = os.environ[key]
            os.environ[key] = value
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        for key in self.mock_vars:
            if key in self.original:
                os.environ[key] = self.original.pop(key)
            else:
                os.environ.pop(key, None)


def get_config_from_env():
    return {
        "host": os.environ.get("APP_HOST", "localhost"),
        "port": int(os.environ.get("APP_PORT", "8080")),
        "debug": os.environ.get("APP_DEBUG", "false").lower() == "true",
    }


if __name__ == "__main__":
    with EnvInjector({"APP_HOST": "example.com", "APP_PORT": "3000", "APP_DEBUG": "true"}):
        print(get_config_from_env())
    print(get_config_from_env())