Sinon stub out 模块的 function

Question

Imagine I have a file here:

// a.js
const dbConnection = require('./db-connection.js')

module.exports = function (...args) {
   // somethin' somethin' ...
   const dbClient = dbConnection.db
   const docs = dbClient.collection('test').find()
 
   if (!docs) {
      return true
   }
}

and I have a test to stub out find() method to return at least true (in order to test out if the a.js 's return value is true. How can I do that?

Answer 1

You can use sinon.stub(obj, 'method') to stub dbConnection.db.collection and its returned value.

Eg

a.js :

const dbConnection = require('./db-connection.js');

module.exports = function () {
  const dbClient = dbConnection.db;
  const docs = dbClient.collection('test').find();

  if (!docs) {
    return true;
  }
};

db-connection.js :

module.exports = {
  // Your real db connection
  db: {
    collection() {
      return this;
    },
    find() {
      return this;
    },
  },
};

a.test.js :

const a = require('./a');
const dbConnection = require('./db-connection.js');
const sinon = require('sinon');

describe('a', () => {
  afterEach(() => {
    sinon.restore();
  });
  it('should find some docs', () => {
    const collectionStub = {
      find: sinon.stub(),
    };
    sinon.stub(dbConnection.db, 'collection').returns(collectionStub);
    const actual = a();
    sinon.assert.match(actual, true);
    sinon.assert.calledWithExactly(dbConnection.db.collection, 'test');
    sinon.assert.calledOnce(collectionStub.find);
  });
});

Test result:

  a
    ✓ should find some docs


  1 passing (6ms)

------------------|---------|----------|---------|---------|-------------------
File              | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
------------------|---------|----------|---------|---------|-------------------
All files         |   77.78 |       50 |   33.33 |   77.78 |                   
 a.js             |     100 |       50 |     100 |     100 | 7                 
 db-connection.js |   33.33 |      100 |       0 |   33.33 | 5-8               
------------------|---------|----------|---------|---------|-------------------