Using VCR and pytest with pytest-recording

pytest-recording is a neat pytest plugin that makes it easy to use the VCR library, which helps write tests against HTTP resources by automatically capturing responses and baking them into a YAML file to be replayed during the tests.

It even works with boto3!

To use it, first install it with pip install pytest-recording and then add the @pytest.mark.vcr decorator to a test that makes HTTP calls:

@pytest.mark.vcr
def test_create():
    runner = CliRunner()
    with runner.isolated_filesystem():
        result = runner.invoke(cli, ["create", "pytest-bucket-simonw-1", "-c"])
        assert result.exit_code == 0

The first time you run the tests, use the --record-mode=once option:

python -m pytest -k test_create --record-mode=once

This defaults to creating a YAML file in tests/cassettes/test_s3_credentials/test_create.yaml.

Subsequent runs of pytest -k test_create will reuse those recorded HTTP requests and will not make any network requests - I confirmed this by turning off my laptop's WiFi.

Filtering out HTTP headers and hiding API keys

For my tests that use API key services like the OpenAI API I've settled on this pattern:

import os
import pytest

API_KEY = os.environ.get("PYTEST_OPENAI_API_KEY") or "fake-key"


@pytest.fixture(scope="module")
def vcr_config():
    return {"filter_headers": ["authorization"]}

The vcr_config() there ensures that any authorization HTTP headers in the resulting cassette YAML files are redacted, so they don't accidentally get checked in to a public GitHub repo.

I use that PYTEST_OPENAI_API_KEY environment variable in tests like this:

@pytest.mark.vcr
def test_ask(monkeypatch):
    monkeypatch.setenv("OPENAI_API_KEY", API_KEY)
    # ...

Then for the duration of that test the OPENAI_API_KEY environment key will either be fake-key for test runs against previously recorded cassette or the value of PYTEST_OPENAI_API_KEY - which means I can update the cassettes like this:

PYTEST_OPENAI_API_KEY=your-key python -m pytest --record-mode once

Created 2021-11-02T17:51:51-07:00, updated 2024-11-24T12:56:52-08:00 · History · Edit

Using VCR and pytest with pytest-recording

Filtering out HTTP headers and hiding API keys

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