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jest-create-mock-instance
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Readme
This library uses jest-mock
internal package to automatically create & instantiate mock for given class/function constructor.
I've been always fan of using sinon.createStubInstance()
in my tests. Unfortunately, Jest doesn't expose similar API to create new mocked instance for given class constructor. Using jest.fn()
or jest's module mocks is not very convienment for various cases, take an example of these classes and unit test:
food.js
export class Food {
consume() {}
}
cat.js
export class Cat {
constructor(food) {
this.food = food;
}
eat() {
this.food.consume();
}
}
and test:
cat.spec.js
import { Food } from "../food";
import { Cat } from "../cat";
let cat;
let food;
beforeEach(() => {
food = new Food();
cat = new Cat(food);
});
it("Must eat", () => {
cat.eat();
expect(food.consume).toBeCalled();
});
By using jest module mocks you must mock your module before and instantiate Food
directly:
jest.mock("../food");
import { Food } from "../food";
beforeEach(() => {
food = new Food();
})
This is very ugly when have many modules to mock (and you don't want automock by default) and when using typescript:
jest.mock("../food1");
jest.mock("../food2");
jest.mock("../food3");
import { Food1 } from "../food1";
import { Food2 } from "../food2";
import { Food3 } from "../food3";
let food1: jest.Mocked<Food1>;
let food2: jest.Mocked<Food2>;
let food3: jest.Mocked<Food3>;
beforeEach(() => {
// Food constructors may have other required parameters so often necessary cast them to any
food1 = new (Food1 as any)() as any;
food2 = new (Food2 as any)() as any;
food3 = new (Food3 as any)() as any;
});
Instead you can just write:
import createMockInstance from "jest-create-mock-instance";
import { Food } from "../food";
let food: jest.Mocked<Food>;
beforeEach(() => {
food = createMockInstance(Food);
});
npm install jest-create-mock-instance --save-dev
createMockInstance
returns jest.Mocked<T>
object. Don't forget to install @types/jest
package.
FAQs
Create class mock instances easily with Jest
The npm package jest-create-mock-instance receives a total of 14,005 weekly downloads. As such, jest-create-mock-instance popularity was classified as popular.
We found that jest-create-mock-instance demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 1 open source maintainer collaborating on the project.
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