Stubbing Redis interactions in javascript using Sinon

Question

I am working in node.js. My app interacts with Redis via the node_redis module. I'm using mocha and sinon to automate testing of my app. My app looks something like this:

...snip
var redisClient = redis.createClient(redisPort, redisHost);
var someValue = redisClient.get("someKey");
return someValue;
....

I want to stub the call to redisClient.get(). To do this I also need to stub the call to redis.createClient() - I think... Here's my test code:

...
var redis = require("redis");
var redisClient;
...
sinon.stub(redisClient, 'get').returns("someValue");
sinon.stub(redis, "createClient").returns(redisClient);
...
assert.equal(redis_client_underTest.call_to_redis(), "someValue");
...

The test fails with AssertionError: false == "someValue"

How do I stub out redisClient, or is this even possible?

Answer 1

What you could do is use something like Proxyquire or Rewire. I'll be using rewire for the example.

Your snippet of code you want to stub:

var redisClient = redis.createClient(redisPort, redisHost);
var someValue = redisClient.get("someKey");
return someValue;

Then in your test you can use rewire:

var Rewire = require('rewire');

var myModule = Rewire("../your/module/to/test.js");

var redisMock = {
    get: sinon.spy(function(something){
             return "someValue";
         });
};

myModule.__set__('redisClient', redisMock);

This way you can have your redisClient replaced and you can check with the spy if the function was called.

Answer 2

Few key points are:

• Stub redisClient before loading main module.
• Stub the CRUD methods for redisClient.

Below is my main module:

/* Main module */
const redis = require('redis');
const redisClient = redis.createClient();

function value(){
  return redisClient.get('someKey');
}

module.exports = {value: value}

Below is my test script:

/* Test */
var sinon = require('sinon');
var redis = require('redis');

// stub redis.createClient

var redisClient = {
    'get': () => "someValue"
}

var redisGetSpy = sinon.spy(redisClient, "get");
var redisClientStub = sinon.stub(redis,
                                 "createClient").callsFake(() => redisClient);

// require main module
var main = require('./main.js');

console.log(main.value(),
            redisClientStub.called,
            redisGetSpy.called, 
            redisGetSpy.callCount);