CODEWITHSUNDEEP
node.jssinonserverless
dirkk
dirkk

Reputation: 6218

Mocking serverless-mysql using sinon

I am trying to test an AWS lambda function (node.js) created using AWS SAM. My function uses the npm module serverless-mysql to connect to Aurora. The following are the relevant parts of my lambda function:

const connection = require('serverless-mysql')({
    config: {
        host     : process.env.DB_HOST,
        user     : process.env.DB_USER,
        password : process.env.DB_PASSWORD
    }
});

exports.lambdaHandler = async (event, context) => {
    try {
        const name = event.pathParameters.name;
        const rows = await connection.query('SELECT * FROM users WHERE name = ?', [name]);
        await connection.end()

        const user = rows[0];
        return {
            'statusCode': 200,
            'body': JSON.stringify({
                firstName: user.first_name,
                lastName: user.last_name,
                bk: user.bk,
                team: user.current_team
            })
        }

    } catch (err) {
        console.log(err);
        return err;
    }
};

I am trying to tests this by mocking the serverless-mysql dependency, but I am currently unable to do so. My test looks like this:

const app = require('../../app.js');
const chai = require('chai');
const sinon = require('sinon');
const expect = chai.expect;
const event = {
    pathParameters: {
        name: 'johndoe'
    }
}
var context;

var successConnectionObject = {
    connect: function() {
        return Promise.resolve();
    },
    query: function(sqlQuery, params) {
        return Promise.resolve('');
    },
    end: function() {} 
}

var mysql = require('serverless-mysql');
var stub = sinon.stub(mysql, 'connect').returns(successConnectionObject);

describe('Tests', function () {
    it('verifies successful response', async () => {
        const result = await app.lambdaHandler(event, context);

        expect(result).to.be.an('object');
        expect(result.statusCode).to.equal(200);
        mock.verify();

        mock.restore();
    });
});

However, this returns the following error:

TypeError: Cannot stub non-existent own property connect

I believe this is because mysql is not instantiated. So I replaced the line var mysql = require('serverless-mysql'); with:

var mysql = require('serverless-mysql')();

Unfortunately, this results in the following error:

AssertionError: expected [Error: Error: self signed certificate in certificate chain] to be an object

So it seems the connect() method of the real serverless-mysql module is called.

How can I correctly mock serverless-mysql using sinon?

Upvotes: 2

Views: 1267

Answers (1)

Brian Adams
Brian Adams

Reputation: 45840

require('serverless-mysql') returns a function that returns a different value each time it is called, so mocking the properties on the result of one call won't affect the returned value of a different call.

That means you have to mock the function itself, which means mocking the entire module.

sinon doesn't provide a way to mock an entire module so you'll have to use something else for that part.

Here is a working test using proxyquire to mock the serverless-mysql module:

const chai = require('chai');
const sinon = require('sinon');
const expect = chai.expect;
const proxyquire = require('proxyquire');

const event = {
  pathParameters: {
    name: 'johndoe'
  }
}
var context;

var successConnectionObject = {
  connect: function () {
    return Promise.resolve();
  },
  query: function (sqlQuery, params) {
    return Promise.resolve([{
      first_name: 'first',
      last_name: 'last',
      bk: 'bk',
      current_team: 'team'
    }]);
  },
  end: function () { }
}

const stub = sinon.stub().returns(successConnectionObject);
const app = proxyquire('../../app.js', { 'serverless-mysql': stub });

describe('Tests', function () {
  it('verifies successful response', async () => {
    const result = await app.lambdaHandler(event, context);

    expect(result).to.be.an('object');  // Success!
    expect(result.statusCode).to.equal(200);  // Success!

    sinon.assert.calledWithExactly(stub, {
      config: {
        host: process.env.DB_HOST,
        user: process.env.DB_USER,
        password: process.env.DB_PASSWORD
      }
    });  // Success!
  });
});

Upvotes: 2

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