How to mock a configuration dependency in TypeScript with Proxyquire?

Question

I have a config.ts which returns an object:

// Config is an interface that I use to know which values are expected
export default function getConfig(): Config {
     return {amount: 50}
}

I have a class (../src/models/item.model) that has a dependency to the config.ts:

import getConfig from '../config/config';

class Item{
    _id: number;
    amount: number;

    constructor(_id: number) {
        this._id = _id;
        this.amount = getConfig().amount;
    }
}

export default Item

I would like to write some tests with a different amount value. The default value is 50 (set in config.ts), but in my item.test.ts I would like to use a value of 100. I'm trying to achieve this by using Proxyquire:

it('should use voxelsize of custom config', (done) => {
    const itemModel = proxyquire('../src/models/item.model', {
        '../config/config': function getConfig() {
            return {amount: 100};
        }
    }).default;

    const testItem = new itemModel(1)

    expect(testItem.amount).to.equal(100);
    done()
})

testItem.amount is in reality 50 (so it still uses the original configuration file). This should be 100.

How can I let the test pass?

Lin Du · Accepted Answer · 2021-03-19 03:24:17Z

You are using es6 export default function getConfig() {}, so you should assign the mocked getconfig() function to the default attribute of the ./config commonJS module.

E.g.

config.ts:

export default function getConfig() {
  return { amount: 50 };
}

item.model.ts:

import getConfig from './config';

class Item {
  _id: number;
  amount: number;

  constructor(_id: number) {
    this._id = _id;
    this.amount = getConfig().amount;
  }
}

export default Item;

item.model.test.ts:

import { expect } from 'chai';
import proxyquire from 'proxyquire';

describe('66691249', () => {
  it('should use voxelsize of custom config', () => {
    const itemModel = proxyquire('./item.model', {
      './config': {
        default: function getConfig() {
          return { amount: 100 };
        },
      },
    }).default;

    const testItem = new itemModel(1);
    expect(testItem.amount).to.equal(100);
  });
});

test result:

  66691249
    ✓ should use voxelsize of custom config (1742ms)


  1 passing (2s)

---------------|---------|----------|---------|---------|-------------------
File           | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
---------------|---------|----------|---------|---------|-------------------
All files      |   83.33 |      100 |      50 |   83.33 |                   
 config.ts     |      50 |      100 |       0 |      50 | 2                 
 item.model.ts |     100 |      100 |     100 |     100 |                   
---------------|---------|----------|---------|---------|-------------------

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