Swagmock — The mock data generator for Swagger (aka OpenAPI)

Subeesh Chothen
Oct 26, 2016 · 3 min read

Swagger (aka OpenAPI) is pretty much the de facto standard to define and describe REST APIs across different platforms. Swagger has been excellent in providing a vendor neutral and language agnostic description format for APIs.

The Swagger specification offers a standard definition, using which, a consumer can understand and interact with the remote service with minimal amount of implementation logic. Swagger, also the world’s most popular REST API description format, has a huge community support including vast number of libraries, frameworks and tooling that very well define the Swagger ecosystem.

When I started using Swagger to build modules for the open source community, I noticed that, there were not much discussions around unit testing guidelines (or best practices) for the swagger ecosystem. I was predominantly working on Node.js support for Swagger, including the modules like swaggerize-express, swaggerize-hapi etc. Even though I was able to use popular unit testing frameworks like mocha and tape to test the swaggerize modules, there wasn’t any module out there, to generate mock data based on the swagger spec.

Why is mock data generation, so important for Swagger spec?

Let’s say, you need to test the input parameter validation for the swagger spec:

swagger: ‘2.0’
version: 0.0.0
title: Simple API
— name: tags
in: query
required: true
type: array
type: string
— name: limit
in: query
required: false
type: integer
format: int32
description: OK

To test the api’s input parameter validations, you need to generate data for tags and limit parameters. The positive test cases, should make sure that tags exists as part of the request (required is true) and limit is optional. Also we need to generate data according to the schema of the parameters. For tags we need an array of string and for limit we need integer numbers.

This makes, data generation (as per the spec), a vital part of the unit test eco system for swagger applications and modules.To summarize, the two important aspects of mock data generation would be,

  • specification The data generated, should strictly follow the specification. Let’s say if you are testing an API that validates numbers, the mock data generator should be able to generate random numbers for a particular parameter.
  • randomness It is important to generate random data, to test, edge case scenarios. Also using random data generator over fixtures, provides the added advantages of increase in code coverage, code readability, and less code maintenance.

So, to test the applications and modules (that deal with Swagger specifications), you need to generate random data based on the spec itself.

Enter Swagmock 🎉🎉🎉

Swagmock provides exactly what we have been looking for — a module to generate mock data based on the Swagger spec. You can generate mock `parameters`, mock `response` data and mock `request`, all adhering to the swagger definition spec, and still, maintaining the randomness aspect of mock data generation.

`Swagmock(api, [options])` initializes a `mockgen` object based on the swagger api. The `api` can be one of the following.

  • A relative or absolute path to the Swagger api document.
  • A URL of the Swagger api document.
  • The swagger api Object
  • A promise (or a `thenable`) that resolves to the swagger api Object

Here is how you can generate mock data for parameters for a route (path)

Generate response mock data

`mockgen.responses(options, [callback])` returns a promise that resolves to mock response object based on the swagger spec.

Generate parameter mock data

`mockgen.parameters(options, [callback])` returns a promise that resolves to mock parameter object based on the swagger spec.

Generate request mock data

`mockgen.requests(options, [callback])` generates the mock request object based on the `options`. `requests` API resolves the `parameters` mock data to generate the `request` mock object useful for unit tests.


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Subeesh Chothen

Written by

wannabe geek. soccer fanatic. wanderlust. opinions expressed are solely my own, and do not express views of my employer

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