OpenAPI Mocking and Testing

🗓️ Last updated on February 23, 2022 | 5 | Improve this page



As OpenAPI emerges as an Open standard and provides way of defining Example Objects , Microcks provides direct support for OpenAPI 3.0 and 3.1.

With this feature, you are able to directly import your OpenAPI specification as a Job within Microcks. Then, it directly discover service definition as well as request/response samples defined as OpenAPI examples. If your specification embeds a JSON or OpenAPI schema definition for your custom datatypes, Microcks will use it for validating received response payload during tests when using the OPEN_API_SCHEMA strategy.


With OpenAPI Example Objects , you are now able to define named example fragments within your OpenAPI specification in YAML or JSON format. In order to produce working mocks, Microcks will need complete request/response samples. So to gather and aggregate fragments into something coherent, the importer will take care of collecting fragments having the same name and re-assemble them into comprehensive request/response pair.


We will illustrate how Microcks uses OpenAPI specification through a Car API sample. The specification file in YAML format can be found here . This API specification was designed using Apicurio , a design studio that supports OpenAPI standards. It is a really simple API that allows registering cars to an owner, listing cars for this owner and adding passenger to a car.

Within this sample specification, we have defined 2 mocks - one for the registering operation and another for the listing cars operation:

  • The POST /owner/{owner}/car operation defines a sample called laurent_307 where we’ll register a Peugeot 307 for Laurent,
  • The GET /owner/{owner}/car operation defines a sample called laurent_cars where we’ll list the cars owned by Laurent.

Specifying request params

Specifying request params encompasses path params, query params and header params. Within our 2 samples, we have to define the owner path param and using our convention introduced above, we have to define it 2 times - one for laurent_307 mock and another for laurent_cars mock.

Path parameters

This is done within the parameters part of corresponding API path, on line 83 of our file. Snippet is represented below:

  - name: owner
    in: path
    description: Owner of the cars
    required: true
      format: string
      type: string
        summary: Value for laurent related examples
        value: laurent
        $ref: '#/components/examples/param_laurent'

One thing to notice here is that Microcks importer supports the use of references like '#/components/examples/param_laurent' to avoid duplication of complex values.

Query parameters

Query parameters are specified using parameters defined under the verb of the specification as you may find on line 20 . Snippet is represented below for the laurent_cars mock:

- name: limit
  in: query
  description: Number of result in page
  required: false
    type: integer
      value: 20

Specifying request payload

Request payload is used within our laurent_307 sample. It is specified under the requestBody of the specification as you may find starting on line 55 . Request payload may refer to OpenAPI schema definitions like in the snippet below:

  description: Car body
        $ref: '#/components/schemas/Car'
          summary: Creation of a valid car
          description: Should return 201
          value: '{"name": "307", "model": "Peugeot 307", "year": 2003}'
  required: true

Specifying response payload

Response payload is used within our laurent_cars sample. It is defined under the Http status of the specification as you may find starting on line 40 . Response payload may refer to OpenAPI schema definitions like in the snippet below:

    description: Success
          type: array
            $ref: '#/components/schemas/Car'
            value: |-
                  {"name": "307", "model": "Peugeot 307", "year": 2003},
                  {"name": "jean-pierre", "model": "Peugeot Traveller", "year": 2017}

And yes… I’ve called one of my car jean-pierre… ;-)

Importing OpenAPI specification

When you’re happy with your API design and example definitions just put the result YAML or JSON file into your favorite Source Configuration Management tool, grab the URL of the file corresponding to the branch you want to use and add it as a regular Job import into Microcks. On import, Microcks should detect that it’s an OpenAPI specification file and choose the correct importer.

Using the above Car API example, you should get the following results:


Using OpenAPI extensions

Starting with version 1.4.0, Microcks proposes custom OpenAPI extensions to specify mocks organizational or behavioral elements that cannot be deduced directly from OpenAPI document.

At the info level of your OpenAPI document, you can add labels specifications that will be used in organizing the Microcks repository . See below illustration and the use of x-microcks extension:

openapi: 3.1.0
  title: OpenAPI Car API
  description: Sample OpenAPI API using cars
    name: Laurent Broudoux
    name: MIT License
  version: 1.1.0
      domain: car
      status: beta
      team: Team A

At the operation level of your OpenAPI document, we could add delay/frequency and dispatcher specifications. These one will be used to customize the dispatching rules to your API mocks. Let’s give an example for OpenAPI using the x-microcks-operation extension:

  summary: Add a car to current owner
  description: Add a car to current owner description
  operationId: addCarOp
    delay: 100
    dispatcher: SCRIPT
    dispatcherRules: |
      def path = mockRequest.getRequest().getRequestURI();
      if (!path.contains("/laurent/car")) {
        return "Not Accepted"
      def jsonSlurper = new groovy.json.JsonSlurper();
      def car = jsonSlurper.parseText(mockRequest.getRequestContent());
      if ( == null) {
        return "Not Accepted"
      return "Accepted"      

Note that we can use multi-line notation in YAML but we will have to escape everything and put \ before double-quotes and \n characters if specified using JSON.

Once labels and dispatching rules are defined that way, they will overwrite the different customizations you may have done through UI or API during the next import of the OpenAPI document.

Still Didn’t Find Your Answer?

Join our community and get the help you need. Engage with other members, ask questions, and share knowledge to resolve your queries and expand your understanding.

Join the community