mocha-using

A smarter way to mock in Mocha.

Description

If you ever find yourself writing large mocked functions that have giant switch/conditional statements used to determine what test is currently happening and how the current mock should respond, this module is for you!

In the background, this module uses proxyquire to handle the mocks. This means the only code values you can mock are require() responses. For me, this really made sense because code should be unmodified when testing and doing coverage reports.

Installing

npm install --save-dev mocha-using

Using

my-module.js

var crypto = require('crypto');

module.exports = function(cb){
    crypto.randomBytes(16, cb);
};

test.js

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

// our stubs (could be in separate file)
const stubs = use => {
    return {
        crypto: {
            randomBytes: function(bytes, cb){
                // we are simply going to look at the `using` object and grab the args the mock
                // should return from that object's `randomBytesResponse` value
                var response_args = 
                    use.randomBytesResponse || 
                    [null, Buffer.from('ffffffffffffffffffffffffffffffff', 'hex')];
                process.nextTick(() => {
                    cb.apply(null, response_args);
                });
            }
        }
    }
};

// note: need to pass the `it` function
const using = require('mocha-using')(it);

// works like a normal require but will use proxyquire to add the stubs
const myModule = using.require('./my-module.js', stubs);

// ready to write our unit tests!
describe('MyModule', () => {
    using({
        randomBytesResponse:[null, Buffer.from('000102030405060708090a0b0c0d0e0f', 'hex')]
    })
    .it('should return 16 random bytes', done => {
        myModule((err, bytes) => {
            if(err) throw err;
            // this would normally be random but, with our stub, we get a consistent value
            expect(bytes.toString('hex')).to.equal('000102030405060708090a0b0c0d0e0f');
            done();
        });
    });
    
    using({
        randomBytesResponse:[new Error('bad juju!')]
    })
    .it('should pass errors back', done => {
        myModule((err, bytes) => {
            expect(err).to.be.instanceOf(Error);
            expect(err.message).to.equal('bad juju!');
            done();
        });
    });
    
    it('should return 16 random bytes', done => {
        myModule((err, bytes) => {
            if(err) throw err;
            // although we didn't pass any data to use for this test, the stub is
            // still active and will use the default
            expect(bytes.toString('hex')).to.equal('ffffffffffffffffffffffffffffffff');
            done();
        });
    });
});

Note: You can also do using().it.only() and using().it.skip() as well!

That mostly sums up the supported functionality. Let me know if you like it or have feature requests/bugs! Thanks for checking out my module!