CODEWITHSUNDEEP
webpackjestjs
thebjorn
thebjorn

Reputation: 27360

How do I test code that depends on a library?

I've created a library mylib that is compiled with the following webpack section:

output: {
    ...
    library: 'mylib',
    libraryTarget: "var",
    libraryExport: 'default',
},

so that it can be included with a script tag and used directly, e.g.:

<script src="mylib.js"></script>
<script>
    mylib.foo();  // the name mylib is available
</script>

In a new app I would like to build on mylib (./src/point.js):

export class Point extends mylib.Widget {
    constructor(x, y) {
        super();
        this.x = x;
        this.y = y;
    }
}

and use jest to write unit tests (./src/__tests__/test-point.js):

import {Point} from "../point";

test("test-point", () => {
    const p = new Point(5, 10);
    expect(p.x).toBe(5);
    expect(p.y).toBe(10);
});

of course jest complains that it doesn't know what mylib is:

(dev) go|c:\srv\lib\dkface> jest
 FAIL  src/__tests__/test-point.js
  ● Test suite failed to run

    ReferenceError: mylib is not defined

      1 |
    > 2 | export class Point extends mylib.Widget {
        |                            ^
      3 |     constructor(x, y) {
      4 |         super();
      5 |         this.x = x;

      at Object.mylib (src/point.js:2:28)
      at Object.<anonymous> (src/__tests__/test-point.js:2:1)

Test Suites: 1 failed, 1 total
Tests:       0 total
Snapshots:   0 total
Time:        4.313s
Ran all test suites.

I'm a bit overwhelmed by the webpack/babel/jest configurations and this is only my second time using jest (the first was on mylib where it works great). How do I get this to work?

Upvotes: 1

Views: 103

Answers (1)

Teneff
Teneff

Reputation: 32148

As you're expecting mylib to be defined as global variable in your environment you can create a setup file and add it into your jest configuration's setupFilesAfterEnv

package.json 
"jest": {
  // ....
  "setupFilesAfterEnv": ['<rootDir>/jest.setup.mylib.js']
}
jest.setup.mylib.js 
// define global variable
global.mylib = jest.genMockFromModule('./src/mylib.js');

Or define it within your test

test-point.js 
import {Point} from "../point";

beforeAll(() => {
  global.mylib = jest.genMockFromModule('./src/mylib.js');
});

But if you have added mylib as a dependency and you have required it into your point

point.js 
const mylib = require('mylib');

then you'll be able to auto mock it within your test

test-point.js 
import {Point} from "../point";

jest.mock('mylib');

test("test-point", () => {
// ....

Upvotes: 1

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