how to stub request.get three times? with 2 same url and 1 different url? - request

Question

I need to write unit testcase for following piece of code. Here urls are external api calls, so I need to mock these. For rest of the testcases I have used sinon. So would like to write these in sinon only.
function 1 {
async.waterfall() {
function 2();
function 3();
}
}
function 2(callback) {
url2_1 = "/calculatorFunctionList"
request.get(url2_1,function (err, res, body) {
return callback("with some diff response")
})}
function 3(callback) {
url3_1 = "addition/values="+somevalue1
url3_2 = "addition/values="+somevalue2
request.get(url3_1,function (err, res, body) {
if(!err) {
request.get(url3_2, function (err, res, body) {
return callback("with some response")
})
}
})
}
I need to stub these requests. How can I do this? Also how and when to call restore for stub so that it won't mess up with other request stub? Currently both stubs are not getting mocked.

Answer 1

Sinon - at its core (forget lolex and nise for a moment) - explicitly deals with stubbing and spying on javascript functions. That's it. It does not concern itself with module loaders or Node per se.
So it does not know how to hook into Node's module loader (require) and stub out dependencies by itself. For the general case, you have two options:
Supply your module (the System-Under-Test) with injection points (say, a function setRequestModule(module){ request = module }, which could be used to supply a Sinon stub.
Use a link-level to intercept calls to the module system to load dependencies and swap them out. See this article on Sinon's how-to section for how to do this.
That was the general case, but since you are dealing with network level stubbing, there is a third option, which is related to the second one, which involves hooking into the http layer in Node and setting up fake requests and responses there using nock.
This would look like this:
const nock = require('nock')
const scope = nock('https://api.github.com')
.get('/repos/atom/atom/license')
.reply(200, {
license: {
key: 'mit',
name: 'MIT License',
spdx_id: 'MIT',
url: 'https://api.github.com/licenses/mit',
node_id: 'MDc6TGljZW5zZTEz',
},
})
This is what I would normally do, but since you insist on only using Sinon you are left with the first option.
Elaboration of the first option: inject dependencies
Your functions 2 and 3 (invalid javascript identifiers, btw) are both dependant on the module request and its method get to have their results. To be able to control what is returned by request.get you would then need to supply your module with a different version of request for your tests. This can be done using dependency injection.
To start with, I assume your function starts with an import of the request module, meaning the first few lines includes a statement looking like this:
const request = require('request');
You would need to change this statement so that the request constant can be replaced, meaning it would now look like this:
let request = require('request');
To be able to control your dependency you can now add a new function to your exports:
module.exports.setRequestModule = function (stub){
request = stub;
}
To use this in your tests you would then need to do this in your tests:
const myModule = require('../src/my-module');
const myRequestStub = {};
myModule.setRequestModule(myRequestStub);
it('should return the expected response', () => {
const expectedOutput = "with some response";
myRequestStub.get = function (url, callback) {
callback(null, expectedOutput);
}
myModule.doSomething() ...
// do test
});
Alternatively
You could also expose the request object in your module:
module.exports._request = request;
You could then, for instance, use sinon to instrument it by stubbing the get method from your tests.
const myModule = require('../src/my-module');
sinon.stub(myModule._request, 'get').callsFake( (url, cb) => cb("hello!") );