CODEWITHSUNDEEP
node.jsunit-testingjestjsmocking
juli1234
juli1234

Reputation: 97

JEST Mock implementation from a builder

Im trying to test something and I cant lead to the solution

const Config = require('client-config')
const cfgM = Config.CFGBuilder.builder().build();

class ConfigService {
  static get(key) {
    return cfgM.getProperty(key);
  }
}

module.exports = ConfigService;

This is what im trying to test. The get from my configManager.

const Config = require('my-config');

const { expect } = chai;
const ConfigService = require('../ConfigService');


jest.mock('my-config', () => ({
  CFGBuilder:
  {
    builder: () => ({
      build: () => ({
        getProperty: jest.fn(),
      }),
    }),
  },
}));

describe('testing config service', () => {
  describe('testing get', () => {
    it('should return db.name', () => {
      Config.CFGBuilder.builder().build().getProperty.mockImplementation(key => 'mykey');
      expect(ConfigService.get('key')).to.be('mykey');
    });
  });
});

The thing is im getting undefined from the ConfigServivce.get('key')

Disclaimer: I didn't code the client-config module. It's just a module I must use

Upvotes: 1

Views: 1911

Answers (1)

Lin Du
Lin Du

Reputation: 102497

You didn't mock a return value or implementation for cfgM.getProperty (), that's why you got undefined. For chain calls of methods, you can use .mockReturnThis() instead of return a nested object.

Here is unit test solution:

index.js:

const Config = require('client-config');
const cfgM = Config.CFGBuilder.builder().build();

class ConfigService {
  static get(key) {
    return cfgM.getProperty(key);
  }
}

module.exports = ConfigService;

index.test.js:

const Config = require('client-config');
const ConfigService = require('./');

jest.mock(
  'client-config',
  () => ({
    CFGBuilder: {
      builder: jest.fn().mockReturnThis(),
      build: jest.fn().mockReturnThis(),
      getProperty: jest.fn(),
    },
  }),
  { virtual: true },
);

describe('testing config service', () => {
  describe('testing get', () => {
    it('should return db.name', () => {
      Config.CFGBuilder.builder()
        .build()
        .getProperty.mockImplementation((key) => 'mykey');
      expect(ConfigService.get('key')).toBe('mykey');
    });
  });
});

unit test result with 100% coverage:

 PASS  stackoverflow/63198582/index.test.js (13.614s)
  testing config service
    testing get
      ✓ should return db.name (3ms)

----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
----------|---------|----------|---------|---------|-------------------
All files |     100 |      100 |     100 |     100 |                   
 index.js |     100 |      100 |     100 |     100 |                   
----------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        15.747s, estimated 18s

Upvotes: 4

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