Chai OpenAPI Response Validator

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Use Chai to assert that HTTP responses satisfy an OpenAPI spec.

Problem 😕

If your server’s behaviour doesn’t match your API documentation, then you need to correct your server, your documentation, or both. The sooner you know the better.

Solution 😄

This plugin lets you automatically test whether your server’s behaviour and documentation match. It extends the Chai Assertion Library to support the OpenAPI standard for documenting REST APIs. In your JavaScript tests, you can simply assert expect(responseObject).to.satisfyApiSpec

Features:

  • Validates the status and body of HTTP responses against your OpenAPI spec (see example)
  • Validates objects against schemas defined in your OpenAPI spec (see example)
  • Load your OpenAPI spec just once in your tests (load from a filepath or object)
  • Supports OpenAPI 2 and 3
  • Supports OpenAPI specs in YAML and JSON formats
  • Supports $ref in response definitions (i.e. $ref: '#/definitions/ComponentType/ComponentName')
  • Informs you if your OpenAPI spec is invalid
  • Supports responses from axios, request-promise, supertest, superagent, and chai-http
  • Bundled with a TypeScript Declaration File for use in TypeScript projects
  • Use in Mocha, Jest and other test runners

Contributing ✨

If you’ve come here to help contribute - thanks! Take a look at the contributing docs to get started.

Installation

This is an addon plugin for the Chai Assertion Library. Install via npm.

npm install --save-dev chai-openapi-response-validator

Usage

In API tests, validate the status and body of HTTP responses against your OpenAPI spec:

1. Write a test:

// Set up Chai
const chai = require('chai');
const expect = chai.expect;

// Import this plugin
const chaiResponseValidator = require('chai-openapi-response-validator');

// Load an OpenAPI file (YAML or JSON) into this plugin
chai.use(chaiResponseValidator('path/to/openapi.yml'));

// Write your test (e.g. using Mocha)
describe('GET /example/endpoint', () => {
  it('should satisfy OpenAPI spec', async () => {
    // Get an HTTP response from your server (e.g. using axios)
    const res = await axios.get('http://localhost:3000/example/endpoint');

    expect(res.status).to.equal(200);

    // Assert that the HTTP response satisfies the OpenAPI spec
    expect(res).to.satisfyApiSpec;
  });
});

2. Write an OpenAPI Spec (and save to path/to/openapi.yml):

openapi: 3.0.0
info:
  title: Example API
  version: 1.0.0
paths:
  /example:
    get:
      responses:
        200:
          description: Response body should be an object with fields 'stringProperty' and 'integerProperty'
          content:
            application/json:
              schema:
                type: object
                required:
                  - stringProperty
                  - integerProperty
                properties:
                  stringProperty:
                    type: string
                  integerProperty:
                    type: integer

3. Run your test to validate your server’s response against your OpenAPI spec:

The assertion passes if the response status and body satisfy openapi.yml:
// Response includes:
{
  status: 200,
  body: {
    stringProperty: 'string',
    integerProperty: 123,
  },
};
The assertion fails if the response body is invalid:
// Response includes:
{
  status: 200,
  body: {
    stringProperty: 'string',
    integerProperty: 'invalid (should be an integer)',
  },
};
Output from test failure:
AssertionError: expected res to satisfy API spec

expected res to satisfy the '200' response defined for endpoint 'GET /example/endpoint' in your API spec
res did not satisfy it because: integerProperty should be integer

res contained: {
  body: {
      stringProperty: 'string',
      integerProperty: 'invalid (should be an integer)'
    }
  }
}

The '200' response defined for endpoint 'GET /example/endpoint' in API spec: {
  '200': {
    description: 'Response body should be a string',
    content: {
      'application/json': {
        schema: {
          type: 'string'
        }
      }
    }
  },
}

In unit tests, validate objects against schemas defined in your OpenAPI spec:

1. Write a test:

// Set up Chai
const chai = require('chai');
const expect = chai.expect;

// Import this plugin
const chaiResponseValidator = require('chai-openapi-response-validator');

// Load an OpenAPI file (YAML or JSON) into this plugin
chai.use(chaiResponseValidator('path/to/openapi.yml'));

// Write your test (e.g. using Mocha)
describe('myModule.getObject()', () => {
  it('should satisfy OpenAPI spec', async () => {
    // Run the function you want to test
    const myModule = require('path/to/your/module.js');
    const output = myModule.getObject();

    // Assert that the output satisfies a schema defined in your OpenAPI spec
    expect(output).to.satisfySchemaInApiSpec('ExampleSchemaObject');
  });
});

2. Write an OpenAPI Spec (and save to path/to/openapi.yml):

openapi: 3.0.0
info:
  title: Example API
  version: 1.0.0
paths:
  /example:
    get:
      responses:
        200:
          description: Response body should be an ExampleSchemaObject
          content:
            application/json:
              schema: '#/components/schemas/ExampleSchemaObject'
components:
  schemas:
    ExampleSchemaObject:
      type: object
      required:
        - stringProperty
        - integerProperty
      properties:
        stringProperty:
          type: string
        integerProperty:
          type: integer

3. Run your test to validate your object against your OpenAPI spec:

The assertion passes if the object satisfies the schema ExampleSchemaObject:
// object includes:
{
  stringProperty: 'string',
  integerProperty: 123,
};
The assertion fails if the object does not satisfy the schema ExampleSchemaObject:
// object includes:
{
  stringProperty: 123,
  integerProperty: 123,
};
Output from test failure:
AssertionError: expected object to satisfy schema 'ExampleSchemaObject' defined in API spec:
object did not satisfy it because: stringProperty should be string

object was: {
    {
      stringProperty: 123,
      integerProperty: 123
    }
  }
}

The 'ExampleSchemaObject' schema in API spec: {
  type: 'object',
  required: [
    'stringProperty'
    'integerProperty'
  ],
  properties: {
    stringProperty: {
      type: 'string'
    },
    integerProperty: {
      type: 'integer'
    }
  }
}

Loading your OpenAPI spec (3 different ways):

1. From an absolute filepath (see above)

2. From an object:

// Set up Chai
const chai = require('chai');
const expect = chai.expect;

// Import this plugin
const chaiResponseValidator = require('chai-openapi-response-validator');

// Get an object representing your OpenAPI spec
const openApiSpec = {
  openapi: '3.0.0',
  info: {
    title: 'Example API',
    version: '0.1.0',
  },
  paths: {
    '/example/endpoint': {
      get: {
        responses: {
          200: {
            description: 'Response body should be a string',
            content: {
              'application/json': {
                schema: {
                  type: 'string',
                },
              },
            },
          },
        },
      },
    },
  },
};

// Load that OpenAPI object into this plugin
chai.use(chaiResponseValidator(openApiSpec));

// Write your test (e.g. using Mocha)
describe('GET /example/endpoint', () => {
  it('should satisfy OpenAPI spec', async () => {
    // Get an HTTP response from your server (e.g. using axios)
    const res = await axios.get('http://localhost:3000/example/endpoint');

    expect(res.status).to.equal(200);

    // Assert that the HTTP response satisfies the OpenAPI spec
    expect(res).to.satisfyApiSpec;
  });
});

3. From a web endpoint:

// Set up Chai
const chai = require('chai');
const expect = chai.expect;

// Import this plugin
const chaiResponseValidator = require('chai-openapi-response-validator');

// Write your test (e.g. using Mocha)
describe('GET /example/endpoint', () => {
  // Load your OpenAPI spec from a web endpoint
  before(async () => {
    const axios = require('axios');
    const response = await axios.get('url/to/openapi/spec');
    const openApiSpec = response.data; // e.g. { openapi: '3.0.0', <etc> };
    chai.use(chaiResponseValidator(openApiSpec));
  });

  it('should satisfy OpenAPI spec', async () => {
    // Get an HTTP response from your server (e.g. using axios)
    const res = await axios.get('http://localhost:3000/example/endpoint');

    expect(res.status).to.equal(200);

    // Assert that the HTTP response satisfies the OpenAPI spec
    expect(res).to.satisfyApiSpec;
  });
});

Using this plugin in a TypeScript project

Installation

You don’t need to npm install --save-dev @types/chai-openapi-response-validator because we bundle our TypeScript Definition file into this package.

But make sure you npm install --save-dev @types/chai because Chai does not bundle their TypeScript definition files like this.

Importing

  1. Make sure your tsconfig.json includes:
{
  "compilerOptions": {
    esModuleInterop: true,
  }
}
  1. Import like this:
import chai from 'chai';
import chaiResponseValidator from 'chai-openapi-response-validator';