How to use printBigInt method in Jest

Thanks to the comment from @jonrsharpe I ran yarn upgrade @types/jest --latest and that resolved my problem. Urgh -- could not see the wood for the trees!

Without using any other libraries:

import * as axios from "axios";

// Mock out all top level functions, such as get, put, delete and post:
jest.mock("axios");

// ...

test("good response", () => {
  axios.get.mockImplementation(() => Promise.resolve({ data: {...} }));
  // ...
});

test("bad response", () => {
  axios.get.mockImplementation(() => Promise.reject({ ... }));
  // ...
});

It is possible to specify the response code:

axios.get.mockImplementation(() => Promise.resolve({ status: 200, data: {...} }));

It is possible to change the mock based on the parameters:

axios.get.mockImplementation((url) => {
    if (url === 'www.example.com') {
        return Promise.resolve({ data: {...} });
    } else {
        //...
    }
});

Jest v23 introduced some syntactic sugar for mocking Promises:

axios.get.mockImplementation(() => Promise.resolve({ data: {...} }));

It can be simplified to

axios.get.mockResolvedValue({ data: {...} });

There is also an equivalent for rejected promises: mockRejectedValue.

Further Reading:

• Jest mocking documentation
• A GitHub discussion that explains about the scope of the jest.mock("axios") line.
• A related question which addresses applying the techniques above to Axios request interceptors.
• Using jest functions like mockImplementation in TypeScript: Typescript and Jest: Avoiding type errors on mocked functions

you 're using "dd'/'M'/'yyyy" format initially,

 (DateTime.Now.ToString("dd'/'M'/'yyyy"))

and "dd/MM/yyyy" format later,

 format: "dd/MM/yyyy"

this is not good.
Use the same format (I suggest "dd/MM/yyyy") in both cases.

Create jest-setup.js file (if already not exists) and add following lines in that

import { NativeModules } from 'react-native';

NativeModules.ReactLocalization = {
    language: 'en',
};

now add this to package.json, now JEST in package.json looks like this.

...
"jest": {
    "preset": "react-native",
    "transformIgnorePatterns": [
      "node_modules/(?!react-native|react)/"
    ],
    "setupFiles": [
      "<rootDir>/jest-setup.js"
    ],
    "globals": {
      "__DEV__": true
    },
    "testEnvironment": "node"
  }
...

Now this error is gone. Source

The delay operator does not work with Jest's fake timers because the delay operator's implementation uses its scheduler's concept of time - which is unrelated to Jest's concept of fake time.

The source is here:

while (queue.length > 0 && (queue[0].time - scheduler.now()) <= 0) {
  queue.shift().notification.observe(destination);
}

The current (non-fake) time is assigned to notifications when they are created and the current time is what the scheduler's now method returns. When Jest's fake timers are used, an insufficient amount of actual (non-fake) time will have elapsed and the notifications will remain in the queue.

To write RxJS tests using fake or virtual time, you can use the VirtualTimeScheduler. See this answer. Or you can use the TestScheduler and marble tests.

It works with ts-jest 24 + it appears to be a bug in my IDE: https://youtrack.jetbrains.com/issue/IDEA-207553

Issue

The docs for toMatchObject states "You can match properties against values or against matchers".

Unfortunately, toBeCloseTo is not currently available as an asymmetric matcher, it looks like these are the only asymmetric matchers currently provided by Jest.

Solution

If you are using Jest v23 or higher you can create your own, essentially duplicating toBeCloseTo using expect.extend:

expect.extend({
  toBeAround(actual, expected, precision = 2) {
    const pass = Math.abs(expected - actual) < Math.pow(10, -precision) / 2;
    if (pass) {
      return {
        message: () => `expected ${actual} not to be around ${expected}`,
        pass: true
      };
    } else {
      return {
        message: () => `expected ${actual} to be around ${expected}`,
        pass: false
      }
    }
  }
});

const foo = {
  bar: 'baz',
  value: 4.9999
};

test('foo', () => {
  expect(foo.value).toBeAround(5, 3);  // SUCCESS in Jest > v20
  expect(foo).toMatchObject({
    bar: 'baz',
    value: expect.toBeAround(5, 3)  // SUCCESS only in Jest > v23
  });
});

Note that expect.extend creates a matcher that can be used within functions like toMatchObject only in Jest v23 and higher.

Alternate Solution

From this post by a Jest collaborator: "Although it is implied but not currently documented, Jest assertions evaluate asymmetric matcher objects as defined in Jasmine".

An asymmetric matcher using the logic from toBeCloseTo can be created like this:

const closeTo = (expected, precision = 2) => ({
  asymmetricMatch: (actual) => Math.abs(expected - actual) < Math.pow(10, -precision) / 2
});

const foo = {
  bar: 'baz',
  value: 4.9999
};

test('foo', () => {
  expect(foo).toMatchObject({
    bar: 'baz',
    value: closeTo(5, 3)  // SUCCESS
  });
});

I've started employing the import * as obj style within my tests, which imports all exports from a module as properties of an object which can then be mocked. I find this to be a lot cleaner than using something like rewire or proxyquire or any similar technique. I've done this most often when needing to mock Redux actions, for example. Here's what I might use for your example above:

import * as network from 'network.js';

describe("widget", function() {
  it("should do stuff", function() {
    let getDataFromServer = spyOn(network, "getDataFromServer").andReturn("mockData")
    let widget = new Widget();
    expect(getDataFromServer).toHaveBeenCalledWith("dataForWidget");
    expect(otherStuff).toHaveHappened();
  });
});

If your function happens to be a default export, then import * as network from './network' would produce {default: getDataFromServer} and you can mock network.default.

Note: the ES spec defines modules as read-only, and many ES transpilers have started honoring this, which may break this style of spying. This is highly dependent on your transpiler as well as your test framework. For example, I think Jest performs some magic to make this work, though Jasmine does not, at least currently. YMMV.

just add jest.useFakeTimers(); after your imports

...
jest.useFakeTimers();

test('demo code', async () => {
        const cc = await projectSetup(project);
        const onNotification = jest.fn();
        cc.sendNotification();
        await waitForExpect(() => {
            expect(onNotification).toHaveBeenCalledTimes(2);
        });

    });

it works in my code