How to Unit Test a Node API using Sinon (Express with Mongo DB)

Question

I am creating an API using Node but am struggling to understand how to properly Unit test the API. The API itself uses Express and Mongo (with Mongoose).

So far I have been able to create Integration tests for end to end testing of the API endpoints themselves. I have used supertest, mocha and chai for the integration tests along with dotenv to use a test database when running it. The npm test script sets the environment to test before the integration tests run. It works excellently.

But I would like to also create Unit Tests for various components such as the controller functions.

I'm keen to use Sinon for the Unit Tests but I'm struggling to know what next steps to take.

I'll detail a genericised version of the API rewritten to be everybody's favourite Todos.

The app has the following directory structure:

api
|- todo
|   |- controller.js
|   |- model.js
|   |- routes.js
|   |- serializer.js
|- test
|   |- integration
|   |  |- todos.js
|   |- unit
|   |  |- todos.js
|- index.js
|- package.json

package.json

{
  "name": "todos",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "directories": {
    "doc": "docs"
  },
  "scripts": {
    "test": "mocha test/unit --recursive",
    "test-int": "NODE_ENV=test mocha test/integration --recursive"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "body-parser": "^1.15.0",
    "express": "^4.13.4",
    "jsonapi-serializer": "^3.1.0",
    "mongoose": "^4.4.13"
  },
  "devDependencies": {
    "chai": "^3.5.0",
    "mocha": "^2.4.5",
    "sinon": "^1.17.4",
    "sinon-as-promised": "^4.0.0",
    "sinon-mongoose": "^1.2.1",
    "supertest": "^1.2.0"
  }
}

index.js

var express = require('express');
var app = express();
var mongoose = require('mongoose');
var bodyParser = require('body-parser');

// Configs
// I really use 'dotenv' package to set config based on environment.
// removed and defaults put in place for brevity
process.env.NODE_ENV = process.env.NODE_ENV || 'development';

// Database
mongoose.connect('mongodb://localhost/todosapi');

//Middleware
app.set('port', 3000);
app.use(bodyParser.urlencoded({extended: true}));
app.use(bodyParser.json());

// Routers
var todosRouter = require('./api/todos/routes');
app.use('/todos', todosRouter);

app.listen(app.get('port'), function() {
    console.log('App now running on http://localhost:' +     app.get('port'));
});

module.exports = app;

serializer.js

(This purely takes the output from Mongo and serializes it into JsonAPI format. So it is a bit superfluous to this example but I left it in as it is something I currently make use of in the api.)

'use strict';

var JSONAPISerializer = require('jsonapi-serializer').Serializer;

module.exports = new JSONAPISerializer('todos', {
    attributes: ['title', '_user']
    ,
    _user: {
        ref: 'id',
        attributes: ['username']
    }
});

routes.js

var router = require('express').Router();
var controller = require('./controller');

router.route('/')
    .get(controller.getAll)
    .post(controller.create);

router.route('/:id')
    .get(controller.getOne)
    .put(controller.update)
    .delete(controller.delete);

module.exports = router;

model.js

var mongoose = require('mongoose');
var Schema = mongoose.Schema;

var todoSchema = new Schema({
    title: {
        type: String
    },

    _user: {
        type: Schema.Types.ObjectId,
        ref: 'User'
    }
});

module.exports = mongoose.model('Todo', todoSchema);

controller.js

var Todo = require('./model');
var TodoSerializer = require('./serializer');

module.exports = {
    getAll: function(req, res, next) {
        Todo.find({})
            .populate('_user', '-password')
            .then(function(data) {
                var todoJson = TodoSerializer.serialize(data);
                res.json(todoJson);
            }, function(err) {
                next(err);
            });
    },

    getOne: function(req, res, next) {
        // I use passport for handling User authentication so assume the user._id is set at this point
        Todo.findOne({'_id': req.params.id, '_user': req.user._id})
            .populate('_user', '-password')
            .then(function(todo) {
                if (!todo) {
                    next(new Error('No todo item found.'));
                } else {
                    var todoJson = TodoSerializer.serialize(todo);
                    return res.json(todoJson);
                }
            }, function(err) {
                next(err);
            });
    },

    create: function(req, res, next) {
        // ...
    },

    update: function(req, res, next) {
        // ...
    },

    delete: function(req, res, next) {
        // ...
    }
};

test/unit/todos.js

var mocha = require('mocha');
var sinon = require('sinon');
require('sinon-as-promised');
require('sinon-mongoose');
var expect = require('chai').expect;
var app = require('../../index');

var TodosModel = require('../../api/todos/model');

describe('Routes: Todos', function() {
  it('getAllTodos', function (done) {
    // What goes here?
  });

  it('getOneTodoForUser', function (done) {
      // What goes here?
  });
});

Now I don't want to test the routes themselves (I do that in the Integration Tests not detailed here).

My current thinking is that the next best thing is to actually unit test controller.getAll or controller.getOne functions. And then to Mock the calls to Mongo via Mongoose using Sinon stubs.

But I have no idea what to do next despite having read the sinon docs :/

Questions

• How do I test controller functions if it requires req, res, next as parameters?
• Do I move the model's find and populate (currently in the Controller function) into todoSchema.static functions?
• How to mock the populate function to do a Mongoose JOIN?
• Basically what goes into test/unit/todos.js to get the above in a solid Unit Test state :/

The end goal is to run mocha test/unit and have it unit test the various parts of that API section

Answer 1

Hi I've created some test for you to understand how to use mocks.

Full example github/nodejs_unit_tests_example

controller.test.js

const proxyquire = require('proxyquire')
const sinon = require('sinon')
const faker = require('faker')
const assert = require('chai').assert

describe('todo/controller', () => {
  describe('controller', () => {

    let mdl
    let modelStub, serializerStub, populateMethodStub, fakeData
    let fakeSerializedData, fakeError
    let mongoResponse

    before(() => {
      fakeData = faker.helpers.createTransaction()
      fakeError = faker.lorem.word()
      populateMethodStub = {
        populate: sinon.stub().callsFake(() => mongoResponse)
      }
      modelStub = {
        find: sinon.stub().callsFake(() => {
          return populateMethodStub
        }),
        findOne: sinon.stub().callsFake(() => {
          return populateMethodStub
        })
      }

      fakeSerializedData = faker.helpers.createTransaction()
      serializerStub = {
        serialize: sinon.stub().callsFake(() => {
          return fakeSerializedData
        })
      }

      mdl = proxyquire('../todo/controller.js',
        {
          './model': modelStub,
          './serializer': serializerStub
        }
      )
    })

    beforeEach(() => {
      modelStub.find.resetHistory()
      modelStub.findOne.resetHistory()
      populateMethodStub.populate.resetHistory()
      serializerStub.serialize.resetHistory()
    })

    describe('getAll', () => {
      it('should return serialized search result from mongodb', (done) => {
        let resolveFn
        let fakeCallback = new Promise((res, rej) => {
          resolveFn = res
        })
        mongoResponse = Promise.resolve(fakeData)
        let fakeRes = {
          json: sinon.stub().callsFake(() => {
            resolveFn()
          })
        }
        mdl.getAll(null, fakeRes, null)

        fakeCallback.then(() => {
          sinon.assert.calledOnce(modelStub.find)
          sinon.assert.calledWith(modelStub.find, {})

          sinon.assert.calledOnce(populateMethodStub.populate)
          sinon.assert.calledWith(populateMethodStub.populate, '_user', '-password')

          sinon.assert.calledOnce(serializerStub.serialize)
          sinon.assert.calledWith(serializerStub.serialize, fakeData)

          sinon.assert.calledOnce(fakeRes.json)
          sinon.assert.calledWith(fakeRes.json, fakeSerializedData)
          done()
        }).catch(done)
      })

      it('should call next callback if mongo db return exception', (done) => {
        let fakeCallback = (err) => {
          assert.equal(fakeError, err)
          done()
        }
        mongoResponse = Promise.reject(fakeError)
        let fakeRes = sinon.mock()
        mdl.getAll(null, fakeRes, fakeCallback)
      })

    })

    describe('getOne', () => {

      it('should return serialized search result from mongodb', (done) => {
        let resolveFn
        let fakeCallback = new Promise((res, rej) => {
          resolveFn = res
        })
        mongoResponse = Promise.resolve(fakeData)
        let fakeRes = {
          json: sinon.stub().callsFake(() => {
            resolveFn()
          })
        }

        let fakeReq = {
          params: {
            id: faker.random.number()
          },
          user: {
            _id: faker.random.number()
          }
        }
        let findParams = {
          '_id': fakeReq.params.id,
          '_user': fakeReq.user._id
        }
        mdl.getOne(fakeReq, fakeRes, null)

        fakeCallback.then(() => {
          sinon.assert.calledOnce(modelStub.findOne)
          sinon.assert.calledWith(modelStub.findOne, findParams)

          sinon.assert.calledOnce(populateMethodStub.populate)
          sinon.assert.calledWith(populateMethodStub.populate, '_user', '-password')

          sinon.assert.calledOnce(serializerStub.serialize)
          sinon.assert.calledWith(serializerStub.serialize, fakeData)

          sinon.assert.calledOnce(fakeRes.json)
          sinon.assert.calledWith(fakeRes.json, fakeSerializedData)
          done()
        }).catch(done)
      })

      it('should call next callback if mongodb return exception', (done) => {
        let fakeReq = {
          params: {
            id: faker.random.number()
          },
          user: {
            _id: faker.random.number()
          }
        }
        let fakeCallback = (err) => {
          assert.equal(fakeError, err)
          done()
        }
        mongoResponse = Promise.reject(fakeError)
        let fakeRes = sinon.mock()
        mdl.getOne(fakeReq, fakeRes, fakeCallback)
      })

      it('should call next callback with error if mongodb return empty result', (done) => {
        let fakeReq = {
          params: {
            id: faker.random.number()
          },
          user: {
            _id: faker.random.number()
          }
        }
        let expectedError = new Error('No todo item found.')

        let fakeCallback = (err) => {
          assert.equal(expectedError.message, err.message)
          done()
        }

        mongoResponse = Promise.resolve(null)
        let fakeRes = sinon.mock()
        mdl.getOne(fakeReq, fakeRes, fakeCallback)
      })

    })
  })
})

model.test.js

const proxyquire = require('proxyquire')
const sinon = require('sinon')
const faker = require('faker')

describe('todo/model', () => {
  describe('todo schema', () => {
    let mongooseStub, SchemaConstructorSpy
    let ObjectIdFake, mongooseModelSpy, SchemaSpy

    before(() => {
      ObjectIdFake = faker.lorem.word()
      SchemaConstructorSpy = sinon.spy()
      SchemaSpy = sinon.spy()

      class SchemaStub {
        constructor(...args) {
          SchemaConstructorSpy(...args)
          return SchemaSpy
        }
      }

      SchemaStub.Types = {
        ObjectId: ObjectIdFake
      }

      mongooseModelSpy = sinon.spy()
      mongooseStub = {
        "Schema": SchemaStub,
        "model": mongooseModelSpy
      }

      proxyquire('../todo/model.js',
        {
          'mongoose': mongooseStub
        }
      )
    })

    it('should return new Todo model by schema', () => {
      let todoSchema = {
        title: {
          type: String
        },

        _user: {
          type: ObjectIdFake,
          ref: 'User'
        }
      }
      sinon.assert.calledOnce(SchemaConstructorSpy)
      sinon.assert.calledWith(SchemaConstructorSpy, todoSchema)

      sinon.assert.calledOnce(mongooseModelSpy)
      sinon.assert.calledWith(mongooseModelSpy, 'Todo', SchemaSpy)
    })
  })
})

routes.test.js

const proxyquire = require('proxyquire')
const sinon = require('sinon')
const faker = require('faker')

describe('todo/routes', () => {
  describe('router', () => {
    let expressStub, controllerStub, RouterStub, rootRouteStub, idRouterStub

    before(() => {
      rootRouteStub = {
        "get": sinon.stub().callsFake(() => rootRouteStub),
        "post": sinon.stub().callsFake(() => rootRouteStub)
      }
      idRouterStub = {
        "get": sinon.stub().callsFake(() => idRouterStub),
        "put": sinon.stub().callsFake(() => idRouterStub),
        "delete": sinon.stub().callsFake(() => idRouterStub)
      }
      RouterStub = {
        route: sinon.stub().callsFake((route) => {
          if (route === '/:id') {
            return idRouterStub
          }
          return rootRouteStub
        })
      }

      expressStub = {
        Router: sinon.stub().returns(RouterStub)
      }

      controllerStub = {
        getAll: sinon.mock(),
        create: sinon.mock(),
        getOne: sinon.mock(),
        update: sinon.mock(),
        delete: sinon.mock()
      }

      proxyquire('../todo/routes.js',
        {
          'express': expressStub,
          './controller': controllerStub
        }
      )
    })

    it('should map root get router with getAll controller', () => {
      sinon.assert.calledWith(RouterStub.route, '/')
      sinon.assert.calledWith(rootRouteStub.get, controllerStub.getAll)
    })

    it('should map root post router with create controller', () => {
      sinon.assert.calledWith(RouterStub.route, '/')
      sinon.assert.calledWith(rootRouteStub.post, controllerStub.create)
    })

    it('should map /:id get router with getOne controller', () => {
      sinon.assert.calledWith(RouterStub.route, '/:id')
      sinon.assert.calledWith(idRouterStub.get, controllerStub.getOne)
    })

    it('should map /:id put router with update controller', () => {
      sinon.assert.calledWith(RouterStub.route, '/:id')
      sinon.assert.calledWith(idRouterStub.put, controllerStub.update)
    })

    it('should map /:id delete router with delete controller', () => {
      sinon.assert.calledWith(RouterStub.route, '/:id')
      sinon.assert.calledWith(idRouterStub.delete, controllerStub.delete)
    })
  })
})

serializer.test.js

const proxyquire = require('proxyquire')
const sinon = require('sinon')

describe('todo/serializer', () => {
  describe('json serializer', () => {
    let JSONAPISerializerStub, SerializerConstructorSpy

    before(() => {
      SerializerConstructorSpy = sinon.spy()

      class SerializerStub {
        constructor(...args) {
          SerializerConstructorSpy(...args)
        }
      }

      JSONAPISerializerStub = {
        Serializer: SerializerStub
      }

      proxyquire('../todo/serializer.js',
        {
          'jsonapi-serializer': JSONAPISerializerStub
        }
      )
    })

    it('should return new instance of Serializer', () => {
      let schema = {
        attributes: ['title', '_user']
        ,
        _user: {
          ref: 'id',
          attributes: ['username']
        }
      }
      sinon.assert.calledOnce(SerializerConstructorSpy)
      sinon.assert.calledWith(SerializerConstructorSpy, 'todos', schema)
    })
  })
})