OpenAPI & Postman - MockServer

Integration testing is a must❗️

Intro

When you're working on a frontend - backend project where the frontend application serves some resources brought in by the backend application, you definitely ran into the issue of frontend team not really being able to work until the backend endpoints are ready. 🤝

For this reason, the API First approach came about. 💯

It states that you should first define the contract between client and server before starting working on implementations.

This way, the two teams can work in parallel as long as they respect that contract.

The backend team knows how it should retrieve the data, and the frontend team knows what to expect as a response to requests. 🚀

Testing

🔵 Backend

In order to do integration testing on the backend side, you can write code that simulates your endpoints being called and/or ( I prefer and) you use Postman to send actual HTTP requests to your BE application.

🔵 Frontend

But can Postman help the FE team too?

The answer is yes!

Postman has the concept of Mock Servers.

First, you need to create some requests calling the BE application.

For each of them, you add some Examples where you specify a mock response for your endpoints.

Then, based on this collection of requests Postman can generate a Mock Server for you.

🔵 Implementation

1️⃣ Generate OpenAPI schema. ( https://app.swaggerhub.com/home)

openapi: 3.0.0
info:
  description: |
    This is a sample Petstore server.  You can find
    out more about Swagger at
    [http://swagger.io](http://swagger.io) or on
    [irc.freenode.net, #swagger](http://swagger.io/irc/).
  version: "1.0.0"
  title: Swagger Petstore
servers:
  - url: 'https://petstore.swagger.io/v2'
tags:
  - name: pet
    description: Everything about your Pets
paths:
  /pet:
    post:
      tags:
        - pet
      summary: Add a new pet to the store
      operationId: addPet
      responses:
        '405':
          description: Invalid input
      requestBody:
        $ref: '#/components/requestBodies/Pet'
    put:
      tags:
        - pet
      summary: Update an existing pet
      operationId: updatePet
      responses:
        '400':
          description: Invalid ID supplied
        '404':
          description: Pet not found
        '405':
          description: Validation exception
      requestBody:
        $ref: '#/components/requestBodies/Pet'
  '/pet/{petId}':
    get:
      tags:
        - pet
      summary: Find pet by ID
      description: Returns a single pet
      operationId: getPetById
      parameters:
        - name: petId
          in: path
          description: ID of pet to return
          required: true
          schema:
            type: integer
            format: int64
      responses:
        '200':
          description: successful operation
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Pet'
            application/xml:
              schema:
                $ref: '#/components/schemas/Pet'
        '400':
          description: Invalid ID supplied
        '404':
          description: Pet not found
    delete:
      tags:
        - pet
      summary: Deletes a pet
      operationId: deletePet
      parameters:
        - name: api_key
          in: header
          required: false
          schema:
            type: string
        - name: petId
          in: path
          description: Pet id to delete
          required: true
          schema:
            type: integer
            format: int64
      responses:
        '400':
          description: Invalid ID supplied
        '404':
          description: Pet not found
components:
  schemas:
    Pet:
      type: object
      required:
        - name
        - photoUrls
      properties:
        id:
          type: integer
          format: int64
        name:
          type: string
          example: doggie
        photoUrls:
          type: array
          xml:
            name: photoUrl
            wrapped: true
          items:
            type: string
        status:
          type: string
          description: pet status in the store
          enum:
            - available
            - pending
            - sold
  requestBodies:
    Pet:
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Pet'
      description: Pet object that needs to be added to the store
      required: true

petstore.json

2️⃣ Import it in Postman.

Import

3️⃣ Add examples to your requests.

4️⃣ Create a mock server based on the Request Collection

And that's it. Let's now test our Mock Server.

Get the Mock Server's URL by clicking on Copy URL.

In my case it's: https://4271e5d3-910d-44ce-8ff3-cdf64991c219.mock.pstmn.io

5️⃣ Go to your terminal and send a request:

curl --location --request GET 'https://4271e5d3-910d-44ce-8ff3-cdf64991c219.mock.pstmn.io/pet/1'  --header 'Accept: application/json'