NodeJS EventEmitter test with Mocha - node.js

Question

I have a problem testing ldapjs client search operation. It returns an EventEmitter that you have to make listen for some specific event. I wrapped this operations to promisify it and to define my logic and I would like to unit-test it.
findUser(username) {
return new Promise((resolve, reject) => {
logger.debug('Searching user: ', username);
this.ldapClient.bind(user.name, .user.password, err => {
if (err) return reject(err);
else
this.ldapClient.search(root, {filter: `(cn=${username})`}, (errSearch, resSearch) => {
if (errSearch) return reject(errSearch);
const entries = [];
resSearch.on('searchEntry', entry => entries.push(entry.object));
resSearch.on('searchReference', referral => reject(new Error(`Received search referall: ${referral}`)));
resSearch.on('error', err => reject((err));
resSearch.on('end', result => {
if (result.status === 0 && entries.length === 1) {
return resolve({
cn: entries[0].cn,
objectclass: entries[0].objectclass,
password: entries[0].password
});
} else {
return reject(new Error(`Wrong search result: ${result}`));
}
});
});
});
});
}
I am using mockery and Sinon to replace ldapjs dependency inside my module:
beforeEach(function () {
searchEM = new EventEmitter();
sandbox = sinon.createSandbox();
ldapClientStub = Stubs.getLdapClientStub(sandbox);
ldapClientStub.bind.yields(null);
ldapClientStub.search.withArgs('o=ldap', {filter: `(cn=${findParam})`}).yields(null, searchEM);
mockery.registerMock('ldapjs', Stubs.getLdapStub(ldapClientStub));
mockery.registerAllowable('../src/client');
UserClientCls = require('../src/client').default;
userClient = new UserClientCls(config.get());
});
it('should return user with given username', function (done) {
setTimeout(() => {
searchEM.emit('searchEntry', users[1]);
searchEM.emit('end', {status: 0});
console.log('emitted');
}, 500);
searchEM.on('end', res => console.log(res));
userClient.findUser(findParam)
.then(user => {
user.cn.should.equal(users[1].attributes.cn);
user.objectclass.should.equal(users[1].attributes.objectclass);
user.password.should.equal(users[1].attributes.password);
return done();
})
.catch(err => done(err));
});
The problem is that listeners defined inside findUser are never called (but the function itself is called). The listener I defined in the test (just to debug the behaviour) is correctly called.
I do not understand if I miss something about how EventEmitters works or if I am doing the test in a wrong way. Or maybe I wrote a bad piece of code that cannot be tested.

Answer 1

I found a solution to my problem. I extended the base EventEmitter: I added the logic to store which event I want to emit and overrode its on method with a logic to emit my fake event.
class TestEventEmitter extends EventEmitter {
constructor() {
super();
}
setFakeEmit(fakeEmit) {
this.fakeEmit = fakeEmit;
}
on(eventName, cb) {
super.on(eventName, cb);
if (super.eventNames().length === 4)
this.fakeEmit.forEach(f => this.emit(f.name, f.obj));
}
}
So, in beforeEach I can stub ldapClientStub.search to make it return my TestEventEmitter:
beforeEach(function() {
searchEM = new TestEventEmitter();
searchEM.setFakeEmit([{
name: 'searchEntry',
obj: { object: users[1].attributes }
}, {
name: 'end',
obj: { status: 0 }
}]);
...
ldapClientStub.search.withArgs('o=ldap', { filter: `(&(cn=${findParam})(objectclass=astsUser))` }).yields(null, searchEM);
})
This solution may be not very elegant, but it works. If someone can post a better solution I'll be glad to have a look.