Prism is a CLI and TypeScript toolkit for various bits of HTTP and API Description functionality.
Learn what these things mean below.
The term "mock" for a lot of developers will have unit-testing connotations. In unit-testing, a mock is a fake implementation of a class or function, which accepts the same arguments as the real thing. It might return something pretty similar to expected output, and different test cases might even modify those returns to see how the code under test works.
This is almost exactly the concept here, just at a HTTP level instead. This is done using a mock server, which will respond to the expected endpoints, error for non-existent endpoints, often even provide realistic validation errors if a client sends it an invalid request.
Prism can be given an OpenAPI v2 or v3 description document, which is essentially a data source for all the decisions Prism makes.
Prism is a HTTP server run from the command-line, so it isn't yet the tool you'll want to use for programmatic mocking in your test-suites. This is planned for the future, so get in touch if you're interested in helping with this.
Read more about this in the Prism mocking guide.
Mocking helps when there is no real API and helps API consumers feel confident they're building applications that will work with the API. Then, when the API has been built, Prism can continue to help by sending proxy requests to the real server and reporting if anything is different.
Running Prism on the CLI with prism proxy openapi.yml http://api.example.com/
will run a HTTP server similar to the mock, and it will use the same
request validation logic as the mock server.
If the request is valid, it will make the same request to the upstream server provided in the CLI, and return its response. At this point, if the response is invalid against the API description provided, it can also error.
Basically, if the consumer makes an invalid request, or the server makes an invalid response, Prism will let you know about it. It can log it, or blow up with errors, you decide which is useful for your use case.
Read more about this in the validation proxy guide.
Prism provides strong support for mocking and validating REST APIs and most structured data types, such as JSON, XML, and URL-encoded forms.
The following content types aren't supported by Prism:
- Multipart requests and responses, such as
multipart/form-data - Binary files, such as PDFs, image files, and zip archives
Both the mock server and the validation proxy server are primarily used via the command-line interface.