class-mocker

Class-mocker is library for mocking dependencies.

Installation

$ npm i --save-dev class-mocker

Usage example

For example you has controller and repository. The controller is curled from the repository.

Repository example

export class UserRepository {
    private readonly data: Map<number, User> = new Map<number, User>();

    constructor() {
        // Initialize data for emulation requests to database
        for (let id = 0; id < 5; id++) {
            this.data.set(id, new User(id, `User${id}`,  `P@$$W0RD`,`user${id}@test-mail.it`));
        }

    }

    async findById(id: number): Promise<User> {
        // Emulate request to database
        await awaitTimeout(1000);
        return this.data.get(id);
    }

    async findAll(): Promise<User[]> {
        // Emulate request to database
        await awaitTimeout(1000);
        return Array.of(...this.data.values())
    }
}

function awaitTimeout(timeout: number): Promise<void> {
    return new Promise<void>(resolve => setTimeout(resolve, timeout));
}

Controller example

export class UserController {
    constructor(private readonly userRepository: UserRepository) {
    }

    async find(id: number): Promise<Response<User | string>> {
        try {
            const user = await this.userRepository.findById(id);

            if (!user) {
                return new Response(404, 'Not found.');
            }

            return new Response(200, user);
        } catch (e) {
            return new Response(500, 'Internal server error.');
        }
    }

    async findAll(): Promise<Response<User[] | string>> {
        try {
            return new Response(200, await this.userRepository.findAll());
        } catch (e) {
            return new Response(500, 'Internal server error.');
        }
    }
}

Mock creation

Mock by return

const userRepositoryMock = new Mock(UserRepository)
    .expect('findAll', {return: []});

Mock on call

const userRepositoryMock = new Mock(UserRepository)
    .expect('findById', {call: (id: number) => {
        expect(id).toBe(2); // Check argument
        return new User(2, 'ReplacedUser2', 'P@$$W0RD', '[email protected]');
    }});

Mock on thrown error

const userRepositoryMock = new Mock(UserRepository)
    .expect('findAll', {throw: new Error('Database is not available')});

Mock by order

const userRepositoryMock = new Mock(UserRepository)
    .expect('findById', {
        at: 1,
        return: new User(4, 'ReplacedUser4', 'P@$$W0RD', '[email protected]'),
    })
    .expect('findById', {at: 2, return: null});

Enjoy!