Typescript, Jest and Axios

I found different posts that tell you how to mock Axios using Jest & Typescript. The only difference in this post is that, when I use Axios, I like to use it as a function rather than calling `axios.get` or `axios.post`.

Imagine you have this Axios request that you want to mock in your tests:

```typescript //src/index.ts import axios from “axios”;

export interface Post { userId: number; id: number; title: string; body: string; }

const DummyRequest = (id: number): Promise => { return axios({ method: “GET”, url: `https://jsonplaceholder.typicode.com/posts/\${id}\`, }).then((response) => { return { …response.data }; }); };

export default DummyRequest; ```

Install jest and jest-ts and initialize jest-ts

```bash

npm i -D ts-jest jest npx ts-jest config:init ```

This last command will create a `jest.config.js` file:

```js //jest.config.js module.exports = { preset: “ts-jest”, testEnvironment: “node”, }; ```

In your tsconfig.json file, make sure that your tests are excluded from the compiler:

```json //tsconfig.json … “exclude”: [ “test/**/*” <—Add this to your exclude array ], … ```

Now we can create a test for our DummyRequest.ts, create this file under `test/index.test.ts`:

```typescript import axios, { AxiosResponse } from “axios”; import DummyRequest from ”../src”; import { mocked } from “ts-jest/dist/util/testing”; //<— This allows to mock results

jest.mock(“axios”); //This is needed to allow jest to modify axios at runtime

it(“returns a post”, async () => { //Arrange const axiosResponse: AxiosResponse = { data: { userId: 1, id: 1, title: “sunt aut facere repellat provident occaecati excepturi optioreprehenderit”, body: “quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto”, }, status: 200, statusText: “OK”, config: {}, headers: {}, };

mocked(axios).mockResolvedValue(axiosResponse); //Mocking axios function rather than a method

//Act const result = await DummyRequest(1);

//Assert expect(result).toBe({ userId: 1, id: 1, title: “sunt aut facere repellat provident occaecati excepturi optioreprehenderit”, body: “quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto”, }); }); ```

Now you can mock the whole Axios function rather than specific methods.