Mocking a Flow.js interface with Jest? - unit-testing

How might a Flow.js interface be mocked with Jest? To my surprise, I haven't found this issue addressed anywhere.
I'm fairly new to both, but the only (untested) option I see is to create a class that inherits from the interface and then mock the implementing class. This seems quite cumbersome and I don't believe I could place the implementing classes (which are what would actually be mocked) inside the __mocks__ folders expected by Jest and still get the expected behavior.
Any suggestions? Is there a more appropriate mocking tool?
Update
Why do I want to create a mock for an interface? This code intends to have a clean separation of the domain and implementation layers, with the domain classes using Flow interfaces for all injected dependencies. I want to test these domain classes. Using a mocking tool could ideally allow me to more easily and expressively modify the behavior of the mocked services and confirm that the domain class being tested is making the appropriate calls to these mocked services.
Here's a simplified example of a class that I would be testing in this scenario. UpdateResources would be the class under test, while ResourceServer and ResourceRepository are interfaces for services that I would like to mock and 'spy' upon:
// #flow
import type { ResourceServer } from '../ResourceServer';
import type { ResourceRepository } from '../ResourceRepository';
/**
* Use case for updating resources
*/
export default class UpdateResources {
resourceServer: ResourceServer;
resourceRepository: ResourceRepository;
constructor(resourceServer: ResourceServer, resourceRepository: ResourceRepository) {
this.resourceServer = resourceServer;
this.resourceRepository = resourceRepository;
}
async execute(): Promise<boolean> {
const updatesAvailable = await this.resourceServer.checkForUpdates();
if (updatesAvailable) {
const resources = await this.resourceServer.getResources();
await this.resourceRepository.saveAll(resources);
}
return updatesAvailable;
}
}
A solution
The approach I've arrived at which seems to work quite well for my purposes is to create a mock implementation of the interface in the __mocks__ directory what exposes jest.fn objects for all implemented methods. I then instantiate these mock implementations with new and skip any use of jest.mock().
__mocks__/MockResourceServer.js
import type { ResourceServer } from '../ResourceServer';
export default class MockResourceServer implements ResourceServer {
getResources = jest.fn(() => Promise.resolve({}));
checkForUpodates = jest.fn(() => Promise.resolve(true));
}
__mocks__/MockResourceRepository.js
import type { ResourceRepository } from '../ResourceRepository';
export default class MockResourceRepository implements ResourceRepository {
saveAll = jest.fn(() => Promise.resolve());
}
__tests__/UpdateResources.test.js
import UpdateResources from '../UpdateResources';
import MockResourceRepository from '../../__mocks__/MockResourceRepository';
import MockResourceServer from '../../__mocks__/MockResourceServer';
describe('UpdateResources', () => {
describe('execute()', () => {
const mockResourceServer = new MockResourceServer();
const mockResourceRepository = new MockResourceRepository();
beforeEach(() => {
jest.clearAllMocks();
});
it('should check the ResourceServer for updates', async () => {
const updateResources = new UpdateResources(mockResourceServer, mockResourceRepository);
await updateResources.execute();
expect(mockResourceServer.checkForUpdates).toHaveBeenCalledTimes(1);
});
it('should save to ResourceRepository if updates are available', async () => {
mockResourceServer.load.mockResolvedValue(true);
const updateResources = new UpdateResources(mockResourceServer, mockResourceRepository);
await updateResources.execute();
expect(mockResourceRepository.saveAll).toHaveBeenCalledTimes(1);
});
it('should NOT save to ResourceRepository if NO updates are available', async () => {
mockResourceServer.load.mockResolvedValue(false);
const updateResources = new UpdateResources(mockResourceServer, mockResourceRepository);
await updateResources.execute();
expect(mockResourceRepository.saveAll).not.toHaveBeenCalled();
});
});
});
If anyone can offer any improvements, I'm open!

The thing is, you don't actually need to mock an implementation of an interface. The purpose of a mock is to 'look like' the real thing, but if you already have an interface that says what the real thing should look like, any implementation that conforms to the interface will automatically serve equally well as a mock. In fact, from the point of view of the typechecker, there won't be a different between the 'real' and the 'mock' implementation.
Personally what I like to do is to create a mock implementation that can be constructed by feeding it mock responses. Then it can be reused in any test case by constructing it directly in that test case with the exact responses it should provide. I.e., you 'script' the mock with what it should say by injecting the responses at the time of construction. The difference between it and your mocking implementation is that if it doesn't have a response, it throws a exception and fails the test. Here's an article I wrote that shows this method: https://dev.to/yawaramin/interfaces-for-scaling-and-testing-javascript-1daj
With this technique, a test case might look like this:
it('should save to ResourceRepository if updates are available', async () => {
const updateResources = new UpdateResources(
new MockResourceServer({
checkForUpdates: [true],
getResources: [{}],
}),
new MockResourceRepository({
saveAll: [undefined],
}),
);
const result = await updateResources.execute();
expect(result).toBeTruthy();
});
What I like about these mocks is that all the responses are explicit, and show you the sequence of calls that are happening.

Related

How to mock Fastify plugin

I am trying to write unit testing for fastify application which also has custom fastify plugin.
Is there a way we can mock fastify plugin? I tried mocking using Jest and Sinon without much success.
Giorgios link to the file is broken, the mocks folder is now absent from the master branch. I dug the commit history to something around the time of his answer and I found a commit with the folder still there. I leave it here for those who will come in the future!
This is what works for me
Setup your plugin according to Fastify docs https://www.fastify.io/docs/latest/Reference/Plugins/
// establishDbConnection.ts
import fp from 'fastify-plugin';
import {FastifyInstance, FastifyPluginAsync} from 'fastify';
import { initDbConnection } from './myDbImpl';
const establishDbConnection: FastifyPluginAsync = async (fastify: FastifyInstance, opts) => {
fastify.addHook('onReady', async () => {
await initDbConnection()
});
};
export default fp(establishDbConnection);
mock the plugin with jest, make sure you wrap the mock function in fp() so that Fastify recognizes it as a plugin.
// myTest.ts
import fp from 'fastify-plugin';
const mockPlugin = fp(async () => jest.fn());
jest.mock('../../../fastifyPlugin/establishDbConnection', (() => {
return mockPlugin;
}));
Your question is a bit generic but if you are using Jest it must be enough for mocking a fastify plugin. You can take a look in this repo and more specifically this file . This is a mock file of fastify and you add the registered plugins and in the specific example addCustomHealthCheck and then in your test files you can just call jest.mock('fastify').
You do not give a specific use case and there are lot of reasons you might want to mock a plugin. The nature of the plugin to be mocked is important to giving a good answer. Because I don't know that specific information I will show how to mock a plugin that creates a decorator that stores data that can be retrieved with fastify.decorator-name. This is a common use case for plugins that connect to databases or store other widely needed variables.
In the below case, the goal is to test a query function that queries a db; a plugin stores the connection information via a fastify decorator. So, in order to unit test the query we specifically need to mock the client data for the connection.
First create an instance of fastify. Next, set up a mock to return the desired fake response. Then, instead of registering the component with fastify (which you could also do), simply decorate the required variables directly with mock information.
Here is the function to be tested. We need to mock a plugin for a database which creates a fastify decorator called db. Specifically, in the below case the function to be tested uses db.client:
const fastify = require("fastify")({ //this is here to gather logs
logger: {
level: "debug",
file: "./logs/combined.log"
}
});
const HOURS_FROM_LOADDATE = "12";
const allDataQuery = `
SELECT *
FROM todo_items
WHERE a."LOAD_DATE" > current_date - interval $1 hour
`;
const queryAll = async (db) => {
return await sendQuery(db, allDataQuery, [HOURS_FROM_LOADDATE]);
};
//send query to db and receive data
const sendQuery = async (db, query, queryParams) => {
var res = {};
try {
const todo_items = await db.client.any(query, queryParams);
res = todo_items;
} catch (e) {
fastify.log.error(e);
}
return res;
};
module.exports = {
queryByAsv
};
Following is the test case. We will mock db.client from the db plugin:
const { queryAll } = require("../src/query");
const any = {
any: jest.fn(() => {
return "mock response";
})
};
describe("should return db query", () => {
beforeAll(async () => {
// set up fastify for test instance
fastify_test = require("fastify")({
logger: {
level: "debug",
file: "./logs/combined.log",
prettyPrint: true
}
});
});
test("test Query All", async () => {
// mock client
const clientPromise = {
client: any
};
//
fastify_test.decorate("db", clientPromise);
const qAll = await queryAll(fastify_test.db);
expect(qAll).toEqual("mock response");
});
});

Aurelia testing components with transient dependencies never uses a mock

We are using the aurelia component testing as defined here (with jest): https://aurelia.io/docs/testing/components#testing-a-custom-element
The component we are testing has a transient dependency. We are creating a mock for this dependency but when we run the tests using au jest, the real one always gets injected by the DI container and never the mock.
Here is the Transient service:
import { transient } from "aurelia-framework";
#transient()
export class ItemService {
constructor() {
}
getItems(): void {
console.log('real item service');
}
}
Here is the 'Mock' service (we have also tried using jest mocks but we get the same result):
import { transient } from "aurelia-dependency-injection";
#transient()
export class MockItemService{
getItems():void {
console.log('mock item service');
}
}
Here is the component under test:
import {ItemService} from "../services/item-service";
import { autoinject } from "aurelia-dependency-injection";
#autoinject()
export class TestElement {
constructor(private _itemService: ItemService) {
}
attached(): void {
this._itemService.getItems();
}
}
Here is the spec file:
import {TestElement} from "../../src/resources/elements/test-element";
import {ComponentTester, StageComponent} from "aurelia-testing";
import {ItemService} from "../../src/resources/services/item-service";
import {MockItemService} from "./mock-item-service";
import {bootstrap} from "aurelia-bootstrapper";
describe('test element', () => {
let testElement;
const path: string = '../../src/resources/elements/test-element';
beforeEach(() => {
testElement = StageComponent.withResources(path).inView(`<test-element></test-element>`);
testElement.bootstrap(aurelia => {
aurelia.use.standardConfiguration();
aurelia.container.registerTransient(ItemService, MockItemService);
});
});
afterEach(() => {
testElement.dispose();
});
it('should call mock item service', async() => {
await testElement.create(bootstrap);
expect(testElement).toBeTruthy();
})
});
But every-time the test is run, the console logs out the real service and not the mock. I have traced this to the aurelia-dependency-injection.js in the Container.prototype.get function. The issue seems to be around this section of code:
var registration = aureliaMetadata.metadata.get(aureliaMetadata.metadata.registration, key);
if (registration === undefined) {
return this.parent._get(key);
}
The registration object seems to be a bit odd, if it was undefined, the code would work as the correct dependency is registered on the parent and it would get the mock dependency. However, it is not undefined therefore it registers the real service in the DI container on this line:
return registration.registerResolver(this, key, key).get(this, key);
The registration object looks like this:
registration = TransientRegistration {_key = undefined}
Is this a bug in aurelia or is there something wrong with what I am doing?
Many Thanks
p.s. GitHub repo here to replicate the issue: https://github.com/Magrangs/aurelia-transient-dependency-issue
p.p.s Forked the DI container repo and added a quick fix which would fix my particular issue but not sure what the knock on effects would be. If a member of the aurelia team could check, that would be good:
https://github.com/Magrangs/dependency-injection/commit/56c7d96a496e76f330a1fc3f9c4d62700b9ed596
After talking to Rob Eisenberg on the issue there is a workaround for this problem. Firstly remove the #transient decorator on the class and then in your app start (usually main.ts) register the class there as a transient.
See the thread here:
https://github.com/Magrangs/dependency-injection/commit/56c7d96a496e76f330a1fc3f9c4d62700b9ed596
I have also updated the repo posted above: https://github.com/Magrangs/aurelia-transient-dependency-issue
to include the fix.
Hopefully this will help any other devs facing the same issue.

Unit testing NestJS controller with request

My Controller function definition looks like that:
async login(#Req() request, #Body() loginDto: LoginDto): Promise<any> {
How I could prepare/mockup Request to provide first argument of function from Jest test?
Inside funciton I am setting headers using request.res.set. Should I somehow pass real Request object to function and then check if header is set or rather mockup whole Request object and check if set function was called?
I managed to do that mocking requests and response using node-mocks-http library.
const req = mocks.createRequest()
req.res = mocks.createResponse()
and then passing this as an argument.
const data = await authController.login(req, loginDto)
expect(req.res.get('AccessToken')).toBe(token.accessToken)
I followed a different approach and instead of using node-mocks-http library I used #golevelup/ts-jest, also, instead of testing if the function returns some value, like res.json() or res.status(), I checked if the function was called with the value I wanted to.
I borrowed this approach from Kent C. Dodds's testing workshop, take a look for similar ideas. Anyway, this is what I did in order to mock the Response dependency of my Controller's route:
// cars.controller.spec.ts
import { createMock } from '#golevelup/ts-jest';
const mockResponseObject = () => {
return createMock<Response>({
json: jest.fn().mockReturnThis(),
status: jest.fn().mockReturnThis(),
});
};
... ommited for brevity
it('should return an array of Cars', async () => {
const response = mockResponseObject();
jest
.spyOn(carsService, 'findAll')
.mockImplementation(jest.fn().mockResolvedValueOnce(mockedCarsList));
await carsController.getCars(response);
expect(response.json).toHaveBeenCalledTimes(1);
expect(response.json).toHaveBeenCalledWith({ cars: mockedCarsList });
expect(response.status).toHaveBeenCalledTimes(1);
expect(response.status).toHaveBeenCalledWith(200);
});
And that's it, I think that the implementation details aren't that important but in any case I'll leave the link to the Github repo where you can find the whole project.

React Native: Jest mocking Platform

When writing unit tests for a React Native project I want to be able to test different snapshots based on different platforms.
I first tried jest.mock to mock Platform but seems to be async. This approach does work when I have two separate files, but I'd prefer to keep everything in one file if possible.
I tried jest.doMock because of this snippet from the documentation:
When using babel-jest, calls to mock will automatically be hoisted to the top of the code block. Use this method if you want to explicitly avoid this behavior.
https://facebook.github.io/jest/docs/en/jest-object.html#jestdomockmodulename-factory-options
However I'm still seeing undesirable results. When I console.log in the android test I see that Platform.OS is whatever I set the first doMock to be.
I also tried wrapping the mock in a beforeEach in a describe becasue I thought that might help with scoping
http://facebook.github.io/jest/docs/en/setup-teardown.html#scoping
describe('ios test', () => {
it('renders ui correctly', () => {
jest.doMock('Platform', () => {
const Platform = require.requireActual('Platform');
Platform.OS = 'ios';
return Platform;
});
const wrapper = shallow(<SomeComponent />);
const tree = renderer.create(wrapper).toJSON();
expect(tree).toMatchSnapshot();
});
});
describe('android test', () => {
it('renders ui correctly', () => {
jest.doMock('Platform', () => {
const Platform = require.requireActual('Platform');
Platform.OS = 'android';
return Platform;
});
const wrapper = shallow(<SomeComponent />);
const tree = renderer.create(wrapper).toJSON();
expect(tree).toMatchSnapshot();
});
});
Any ideas on how I can change the mock Platform for tests in the same file?
There are a lot of suggestions on how to solve this problem in another question, but none of them worked for me either, given the same requirements you have (tests for different OSs in the same suite file and in one test run).
I eventually worked around it with a somewhat clunky trivial helper function that can be mocked as expected in tests – something like:
export function getOS() {
return Platform.OS;
}
Use it instead of Platform.OS in your code, and then simply mock it in your tests, e.g.
it('does something on Android', () => {
helpers.getOS = jest.fn().mockImplementationOnce(() => 'android');
// ...
}
That did the trick; credit for the idea is due to this guy.

How do you mock a service in AngularJS when unit testing with jasmine?

Let's say I have a service shop that depends on two stateful services schedule and warehouse. How do I inject different versions of schedule and warehose into shop for unit testing?
Here's my service:
angular.module('myModule').service('shop', function(schedule, warehouse) {
return {
canSellSweets : function(numRequiredSweets){
return schedule.isShopOpen()
&& (warehouse.numAvailableSweets() > numRequiredSweets);
}
}
});
Here are my mocks:
var mockSchedule = {
isShopOpen : function() {return true}
}
var mockWarehouse = {
numAvailableSweets: function(){return 10};
}
Here are my tests:
expect(shop.canSellSweets(5)).toBe(true);
expect(shop.canSellSweets(20)).toBe(false);
beforeEach(function () {
module(function ($provide) {
$provide.value('schedule', mockSchedule);
});
});
Module is a function provided by the angular-mocks module. If you pass in a string argument a module with the corresponding name is loaded and all providers, controllers, services, etc are available for the spec. Generally they are loaded using the inject function. If you pass in a callback function it will be invoked using Angular's $injector service. This service then looks at the arguments passed to the callback function and tries to infer what dependencies should be passed into the callback.
Improving upon Atilla's answer and in direct answer to KevSheedy's comment, in the context of module('myApplicationModule') you would do the following:
beforeEach(module('myApplicationModule', function ($provide) {
$provide.value('schedule', mockSchedule);
}));
With CoffeeScript I run in some issues so I use null at the end:
beforeEach ->
module ($provide) ->
$provide.value 'someService',
mockyStuff:
value : 'AWESOME'
null
You can look here for more info
https://docs.angularjs.org/guide/services#unit-testing
You want to utilize the $provide service. In your case
$provide.value('schedule', mockSchedule);
As you are using jasmine, there is an alternative way to mock the calls with jasmine's spies (https://jasmine.github.io/2.0/introduction.html#section-Spies).
Using these you can be targeted with your function calls, and allow call throughs to the original object if required. It avoids clogging up the top of your test file with $provide and mock implementations.
In the beforeEach of your test I would have something like:
var mySchedule, myWarehouse;
beforeEach(inject(function(schedule, warehouse) {
mySchedule = schedule;
myWarehouse = warehouse;
spyOn(mySchedule, 'isShopOpen').and.callFake(function() {
return true;
});
spyOn(myWarehouse, 'numAvailableSweets').and.callFake(function() {
return 10;
});
}));
and this should work in similar fashion to the $provide mechanism, noting you have to provide local instances of the injected variables to spy on.
I recently released ngImprovedTesting module that should make mock testing in AngularJS way easier.
In your example you would only have to replace in your Jasmine test the ...
beforeEach(module('myModule'));
... with ...
beforeEach(ModuleBuilder.forModule('myModule').serviceWithMocks('shop').build());
For more information about ngImprovedTesting check out its introductory blog post:
http://blog.jdriven.com/2014/07/ng-improved-testing-mock-testing-for-angularjs-made-easy/
It is simpler to put the mock on the module like this:
beforeEach(function () {
module('myApp');
module({
schedule: mockSchedule,
warehouse: mockWarehouse
}
});
});
you can use injection to get reference to these mocks for pre test manipulations :
var mockSchedule;
var mockWarehouse;
beforeEach(inject(function (_schedule_, _warehouse_) {
mockSchedule = _schedule_;
mockWarehouse = _warehouse_;
}));
I hope my answer is not that useless, but you can mock services by $provide.service
beforeEach(() => {
angular.mock.module(
'yourModule',
($provide) => {
$provide.service('yourService', function() {
return something;
});
}
);
});