Cornell: record & replay mock server
Cornell makes it dead simple, via its record and replay features to perform end-to-end testing in a fast and isolated testing environment.
When your application integrates with multiple web-based services, end-to-end testing is crucial before deploying to production. Mocking is often a tedious task. It becomes even more tiresome when working with multiple APIs from multiple vendors.
vcrpy is an awesome library that records and replays HTTP interactions for unit tests. Its output is saved to reusable "cassette" files.
By wrapping vcrpy with Flask, Cornell provides a lightweight record and replay server that can be easily used during distributed system testing and simulate all HTTP traffic needed for your tests.
Basic Use Case
When you're working with distributed systems, the test client entry point triggers a cascade of events that eventually send HTTP requests to an external server
With Cornell server started, it will act as a proxy (record mode) between the outgoing HTTP requests and the external server and will record all relevant interactions. Once interactions are recorded, Cornell can work in replay mode, replacing the external server entirely, short-circuiting the calls and instead, replying back instantly with the previously recorded response.
To install from PyPI, all you need to do is this:
pip install cornell
Usage: cornell_server.py [OPTIONS] Usage Examples: Record mode: `cornell --forward_uri="https://remote_server/api" --record -cd custom_cassette_dir` Replay mode: `cornell -cd custom_cassette_dir Options: -p, --port INTEGER -ff, --forward_uri TEXT Must be provided in case of recording mode -, --record-once / --record-all Record each scenario only once, ignore the rest -r, --record Start server in record mode -fp, --fixed-path Fixed cassettes path. If enabled, Cornell will support only one server for recording -cd, --cassettes-dir TEXT Cassettes parent directory, If not specified, Cornell parent dir will be used -re, --record-errors BOOLEAN If enabled, Cornell will record erroneous responses --help Show this message and exit.
Demo - Full Example
Start Cornell in record mode:
cornell -ff https://api.github.com/ --record -cd cassettes
This will start the server in record-proxy mode on port
9000, and will forward all requests to
When cornell is in record mode, it will forward all request to the specified forwarding URL, for example:
or you can browse to the URL using your browser
Cornell will forward the request to the specified URL and will record both the request and the response.
The yaml cassettes will be recorded to a dedicated directory (by default,
cassettes in the root dir)
By default, `cassettes` directory will be created in cornell's root dir and will contain the cassette by destination hierarchy. Use `-cd` to specify custom directory for your cassettes. Mind that `-cd <custom_dir> should match for both record and replay modes
Once all the necessary interactions were recorded, stop cornell server using ctrl+c.
Once stopped, all interactions will be mapped via an auto-generated
In case the `index.yaml` is already present, it will be updated with new interactions. Otherwise, a new file will be created.
Cornell doesn't record interactions with an erroneous response, by default (i.e response with 404, will omitted). If you wish to enable this option, run cornell with --record-errors flag
In this specific example, we can see that the 2 requests are mapped to the saved cassettes:
Start cornell as docker container
docker run hiredscorelabs/cornell:latest
Build cornell as docker container
docker build -t cornell . docker run cornell --help
You will probably need to import cassettes from a local directory from your computer. To do that, use the following command to mount a local directory as a volume in the container.
docker run -v ~/cassettes:/var/cassettes cornell -cd /var/cassettes
In some case, you want to use another port with cornell. If you need to do that, you should use
docker port mapping as in the following where cornell will listen on port
docker run -p 9020:9000 cornell
In addition to the vcrpy matchers, cornell provides the following custom request matchers:
Since Cornell is a testing server it's executed by default with
You can modify this as described in flask configuration
Can be found in the documentation
Yes please! contributions are more than welcome!
Add tests when you're adding new functionality and make sure all the existing tests are happy and green :)
To set up development environment:
python -m venv venv source venv/bin/activate make configure
To run tests, run the following command
python -m venv venv source venv/bin/activate make test