Async testing with Jest

PHOTO EMBED

Mon Dec 07 2020 13:14:38 GMT+0000 (UTC)

Saved by @eneki

// SCRIPT.JS

// const fetch = require("node-fetch")
// Was originally called here but is now called in the test

const getPeople = (fetch) => {
    return fetch("https://swapi.dev/api/people")
        .then(res => res.json())
        .then(data => {
            return {
                count: data.count,
                results: data.results
            }
        }).catch(err => err)
}

const isCity = (city, db) => {
    return db.includes(city)
    // Returns truthy or falsy
}
module.exports = {
    getPeople, 
    isCity
}

// SCRIPT.TEST.JS (that is a naming convention: file-name.test.js)
// Destructuring
const {getPeople, isCity} = require("./script")
const fetch = require("node-fetch")


test("calls swapi to get people with a promise", () => {
    expect.assertions(2)
    return  getPeople(fetch) 
        .then(data => {
            expect(data.count).toEqual(82)
            expect(data.count).not.toEqual(42)
        })
})


//Capture calls
test("testing captured calls", () => {
    const mock = jest.fn()

    let result = mock("foo")

    expect(mock).toHaveBeenCalled()
    expect(mock).toHaveBeenCalledTimes(1)
    expect(mock).toHaveBeenCalledWith("foo")
})

// Set return values
test("mock return value", () => {
    const mock = jest.fn()

    mock.mockReturnValue("bar")

    expect(mock("foo")).toBe("bar")
    expect(mock).toHaveBeenCalledWith("foo")
})

// Replace implementation of dependency (in this case, node-fetch)
test("test getPeople with dependency injection", () => {
    const mockFetch = jest.fn()
        .mockReturnValue(Promise.resolve({
            json: () => Promise.resolve({
                count: 87,
                results: [1,2,3,4,5]
            })
        }))
    expect.assertions(5)
    return getPeople(mockFetch).then(data => {
        expect(mockFetch.mock.calls.length).toEqual(1)
        expect(mockFetch).toHaveBeenCalled()
        expect(mockFetch).toHaveBeenCalledTimes(1)
        expect(mockFetch).toHaveBeenCalledWith("https://swapi.dev/api/people")
        expect(data.count).toEqual(87)
    })
})

let db = []

const initDb = () => db = ["Vienna", "London", "San Juan", "Medllin"]
const closeDb = () => db = []

//  To init before each and close after each

beforeEach(() => initDb())
afterEach(() => closeDb())
beforeAll(() => initDb())
afterAll(() => closeDb())

test("city db has Vienna", () => {
    expect(isCity("Vienna", db)).toBeTruthy()
})
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