Prevent the necessity of typecasting in mocked TypeScript imports

When I import a mocked function, Typescript doesn't recognize that Jest changes the import to a mock. As a result, I have to cast the imported function in order to utilize mock methods such as mockReturnValue.

jest.mock('../myImport');
import { thisFunctionIsMocked } from '../myImport'

/* ... */

(<Mock<any>>thisFunctionIsMocked).mockReturnValue(42);

If I don't cast the import, Typescript gives an error claiming that the mock function methods do not exist. Is there a more efficient way to handle this situation?

Answer №1

I've been searching for a solution to this same issue. It appears there isn't much information available on how to tackle it, but there are a few alternatives to consider.

1) Try using a slightly different syntax from what you're currently using:

(thisFunctionIsMocked as jest.Mock).mockReturnValue(42);

2) Another option is to use require and cast the function there:

const thisFunctionIsMocked = require('../myImport') as jest.Mock;

Update:

The ts-jest now provides a mocked helper that can be utilized. This ensures that the type signature of the original source remains intact even when referencing mocked imports:

import { mocked } from 'ts-jest/utils';

test('direct', () => {
  foo.name();
  expect(mocked(foo.name).mock.calls).toHaveLength(1);
});

Answer №2

Inspired by @lobati's solution, here is a modified approach for handling mock modules with multiple exports:

import * as myModuleMock from 'path/to/my/module';
const { someExport, someOtherExport } = 
    require('path/to/my/__mocks__/module') as typeof myModuleMock;

// The types of `someExport` and `someOtherExport` will be inferred correctly 
/// based on the type information provided in the actual mock

By utilizing this method, there is no need to duplicate type information from the mock module or manage each export individually.

Answer №3

In order to easily and cleanly apply mocks until Jest can intercept ES6 modules, I found this method to be the most suitable for my specific situation.

jest.mock('./some/resource', () => ({
  thisFunctionIsMocked: jest.fn()
})

const { thisFunctionIsMocked } = require('./some/resource');

test('works', () => {
  thisFunctionIsMocked.mockReturnValue('cool result');
  expect(thisFunctionIsMocked()).toEqual('cool result');
});

It's important to point out the usage of require instead of import.

If you are incorporating module mocks, make sure to export them using CommonJS syntax:

module.exports = {
  thisFunctionIsMocked: jest.fn()
};

Once again, this is due to Jest not being able to intercept ES6 modules as of now.

Answer №4

When it comes to module augmentation, there are certain limitations you need to be aware of. For instance, if you export a function in a certain way, you may not be able to modify existing types.

export function thisFunctionIsMocked() { .... }

This is because types can only be added to, not altered. However, if you export your function like this:

export interface MyMockedFunction {
    (): void;
}

export const thisFunctionIsMocked = function() { ... } as MyMockedFunction;

You can then proceed to augment it accordingly:

jest.mock('../myImport');
import { thisFunctionIsMocked } from '../myImport'

declare module "../myImport" {
    interface MyMockedFunction {
        mockReturnValue(value: number): any;
    }
}

thisFunctionIsMocked.mockReturnValue(42);

Similar questions

If you have not found the answer to your question or you are interested in this topic, then look at other similar questions below or use the search

Error TS2339: The attribute 'scope' is not found in the 'JwtPayload' data type

Encountering an error in my IntelliJ IDE while trying to utilize decodedJwt.scope. The specific error message reads: Property 'scope' is not available on type 'JwtPayload'. Suggestions offered by IntelliJ include: sub, aud, exp, iat, ...

The colors of the active Svelte Carousel navigation dots do not smoothly transition along with the slides

Currently, I am developing a carousel feature using schadcn-svelte and embla carousel. Everything seems to work fine initially - when clicking on dot 2, it transitions smoothly from slide 1 to slide 2, and the active dot styles update correctly. However, a ...

AngularJS Currency Converter - Converting Currencies with Ease

I have a question regarding the most efficient way to handle currency conversion on a webpage. Currently, I have multiple input fields displaying different currencies. When a user clicks on the currency conversion button, a modal popup appears. After the ...

The data type 'string' cannot be assigned to the type 'SystemStyleObject | undefined' in the context of Next.js and Chakra UI

I am currently working on a project that involves Next.js, TypeScript, and Chakra UI. While configuring Button themes in the button.ts file, I encountered an error related to the baseStyle object for properties like borderRadius, color, and border: Type & ...

The FirebaseX Ionic native plugin received 2 arguments instead of the expected 3-4

Trying to implement Firebase Phone Auth with the FirebaseX plugin, I encountered an issue. Here is the code snippet I used: async getVerificationCode(): void { const res:any = await this.firebaseX.verifyPhoneNumber('+16505553434', 60); ...

Start incrementing from the value of x

I'm trying to create an incremental column in Node.js with TypeORM, similar to this: @Column() @Generated('increment') public orderNumber: number; Is there a method to set TypeORM to begin counting from 9000 instead of the default starting ...

Incorporate a JavaScript array into a TypeScript document

Having a file named array.js with a large collection of strings, structured like this: module.exports = ["word1","word2",...] I attempted to utilize this array in my validation.ts file by adding the following line: let wiki = require('./array.js&a ...

Exploring an array in Angular 2 using TypeScript

Just starting out with typescript and angular2 and working through some issues. I have a form that needs to display results from an array of changing items, so I don't know the exact index of each result. Here is my scenario: In my form.html file: ...

Assign a specific value to each object

Receiving data from the backend in a straightforward manner: this.archiveService.getRooms(team).subscribe( res => { this.form = res; this.form.forEach(el => { el.reservation.slice(-6).match(/.{1,2}/g).join('/'); }); }, ...

What causes TypeScript to flag spread arguments within callback wrappers?

My aim is to enhance a callback function in TypeScript by wrapping it with additional logic. In order to achieve this, I have an interface called Callbacks that outlines various callback signatures. The objective is to create a wrapper function that can lo ...

Exploring the Possibilities with Material UI v4: Expanding on PaletteColor

Looking to make a simple adjustment in Material UI v4's (v4.11) palette, specifically adding a new field to PaletteColorOptions like darker?: string. The type definition can be found in the relevant Material UI module: createPalette.d.ts export type ...

Using TypeScript along with Nuxt.js and Vuex to access methods from an imported class

Currently, I am in the process of developing a nuxt.js application with typescript and my goal is to segregate the API Calls from the vuex store. However, I've encountered an issue where it seems like I cannot utilize the methods when importing the cl ...

What steps should I take to resolve the issue of 'unable to locate the name 'OktaAuthService' error?

I am currently trying to incorporate authentication into an Angular application using Okta. I have carefully followed the step-by-step instructions provided in the documentation at this link: . However, I am encountering an error when attempting to start t ...

Discovering the RootState type dynamically within redux toolkit using the makeStore function

I am currently working on obtaining the type of my redux store to define the RootState type. Previously, I was just creating and exporting a store instance following the instructions in the redux toolkit documentation without encountering any issues. Howev ...

Leverage the nativeElement property within two separate components

Encountering an error in the autocomplete feature for Angular Maps (AGM), which reads: ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'nativeElement' of undefined TypeError: Cannot read property 'nativeElement' of ...

Developing a TypeScript PureMVC project from scratch

Currently, I am working on a project to implement PureMVC in TypeScript using npm and grunt. Unfortunately, PureMVC has ended development on their project and there is a lack of resources for PureMVC in TypeScript online. The documentation only provides in ...

Testing Angular Components - Creating Mocks for AngularFireStore Collection Fetching

Update I made some progress today, but I've encountered a new error in the same process. Updated question below. I'm here with another query regarding how to simulate a complex call from AngularFireStore. I'm facing an issue while running ...

Is it possible to globally modify the component reference <dropdown-component> name in Angular during runtime in a dynamic manner?

I am currently working on an application that utilizes a component called "dropdown-component" throughout its pages. However, due to specific business requirements, I have been tasked with replacing "dropdown-component" with "custom-dropdown-component". Un ...

Embarking on your ABLY journey!

Incorporating https://github.com/ably/ably-js into my project allowed me to utilize typescript effectively. Presently, my code updates the currentBid information in the mongodb document alongside the respective auctionId. The goal is to link the auctionId ...

What is the most efficient way to update data multiple times by mapping over an array of keys in a react hook?

My question might not be articulated correctly. I'm facing an issue with dynamically translating my webpage using Microsoft's Cognitive Services Translator. I created a react hook for the translator, which works well when I need to translate a si ...