How to mock dayjs chained methods

Question

I have this dayjs objects:

const today = dayjs.utc(date).startOf("day")

I am trying to mock it using jest but to no avail. Here is the approach I tried:

jest.mock("dayjs", () => ({
  extend: jest.fn(),
  utc: jest.fn((...args) => {
    const dayjs = jest.requireActual("dayjs");
    dayjs.extend(jest.requireActual("dayjs/plugin/utc"));

    return dayjs
      .utc(args.filter((arg) => arg).length > 0 ? args : mockDate)
      .startOf("day");
  }),
  startOf: jest.fn().mockReturnThis(),
}));

I also tried this:

jest.mock("dayjs", () => ({
  extend: jest.fn(),
  utc: jest.fn((...args) => ({
    startOf: jest.fn(() => {
      const dayjs = jest.requireActual("dayjs");
      dayjs.extend(jest.requireActual("dayjs/plugin/utc"));

      return dayjs
        .utc(args.filter((arg) => arg).length > 0 ? args : mockEventData)
        .startOf("day");
    }),
  })),
}));

Both are not working. Anyone got an advice?

Gessner

Shouldn't it be utc(...args) instead of utc(args)? What exactly does 'not working' mean? If there are errors, please, show them. The question should contain a clear problem statement and a way to reproduce the problem. – Castoff

@Gessner Can you share the working example? Also, how can I mock the default dayjs() function within current implementation? – Kinesics

What is mockDate and mockDateData for your args above? – Caucasus

Answer 1

Presuming you're trying to create a consistent output disregarding the given date argument, you can create Node Module mock like this:

src/__mocks__/dayjs.js

const mock = jest.genMockFromModule('dayjs');

const dayjs = jest.requireActual("dayjs");
const utc = jest.requireActual('dayjs/plugin/utc')
dayjs.extend(utc);

mock.utc = jest.fn().mockReturnValue(dayjs.utc(new Date('1995-12-17T03:24:00')))

module.exports = mock;

and then in your tests within the src folder dayjs.utc will always be using the mocked date

src/today.spec.js

const today = require("./today");
const dayjs = require("dayjs");

describe("today", () => {
  let result;
  beforeAll(() => {
    result = today();
  });

  it("should be called with a date", () => {
    expect(dayjs.utc).toHaveBeenCalledWith(expect.any(Date));
  });

  it("should return consistent date", () => {
    expect(result).toMatchInlineSnapshot(`"1995-12-17T00:00:00.000Z"`);
  });
});

example on github

Electrotherapy

I've discovered that my initial approach was actually working (with small modification), I was just feeding it the wrong input data. But thanks for the answer, it sure is a valid approach, albeit different. – Gessner

Answer 2

The best solution that I found is using jest fake timers, see docs.

describe('myDayjsFunction', () => {
  it('returns my value', () => {
    const param = 3

    jest.useFakeTimers().setSystemTime(new Date('2023-01-10'))

    const actual = myDayjsFunction(param)
    const expected = 5

    expect(actual).toEqual(5)

    jest.useRealTimers()
  })
})

Peltate

Answer 3

MockDate works great for this, no intense mocking code required.

https://www.npmjs.com/package/mockdate

import MockDate from 'mockdate'
import dayjs from 'dayjs'
import utc from 'dayjs/plugin/utc'
dayjs.extend(utc)

MockDate.set('2000-11-22')
console.log(dayjs.utc().format())

// >>> 2000-11-22T00:00:00Z

Remember to clear the mock after your test with: MockDate.reset();

Towery

Answer 4

I'm using plugin customParseFormat and I just mock like this:

jest.mock('dayjs/plugin/customParseFormat', () => ({
  default: jest.requireActual('dayjs/plugin/customParseFormat'),
}));

It works for me.

Conclusion

Answer 5

I've solved my problem with expect.any(Date) in a simple way! When I need to do an update, I record the actual date and in the test I used the expect.any(Date) to see if any date have been passed on query in the updatedAt field.

expect(prisma.transaction.update).toBeCalledWith({
    where: {
      id: 'any_id'
    },
    data: {
      error: 'Error message here',
      tries: 1,
      updatedAt: expect.any(Date)
    }
});

Strangle