Testing Promises with multiple thens using testdoublejs - node.js

Question

I am using testdouble for stubbing calls within my node.js project. This particular function is wrapping a promise and has multiple then calls within the function itself.
function getUser (rethink, username) {
return new Promise((resolve, reject) => {
let r = database.connect();
r.then(conn => database.table(tablename).filter({username}))
.then(data => resolve(data))
.error(err => reject(err));
});
}
So I am wanting to determine if the resolve and reject are handled correctly based on error conditions. Assume there is some custom logic in there that I need to validate.
For my test
import getUser from './user';
import td from 'testdouble';
test(t => {
const db = td.object();
const connect = td.function();
td.when(connect('options')).thenResolve();
const result = getUser(db, 'testuser');
t.verify(result);
}
The issue is that the result of connect needs to be a promise, so I use then resolve with a value which needs to be another promise that resolves or rejects.
The line it is relating to is the result of database.connect() is not a promise.
TypeError: Cannot read property 'then' of undefined
Anyone have success with stubbing this type of call with Test Double?

Answer 1

So figured out the resolution. There are a few things to note in the solution and that we encountered. In short the resolution ended up being this...
td.when(database.connect()).thenResolve({then: (resolve) => resolve('ok')});
This resolves a thenable that is returned when test double sees database connect. Then subsequent calls can also be added.
There is also a part to note if you send in an object to database.connect() you have to be aware that it is doing === equality checking and you will need to have a reference to that object for it to correctly use td.when.

Answer 2

Test double provides stubs for unit testing. And in your case 'db' is the object we need to mock. Creating the mocking db through
td.object(Database) // Database is the class or constructor of your db
will be the right choice, but to simply mock those methods you need in this case, I wouldn't pick that way.
Here's the tested module, 'some.js':
function getUser (database, username) {
return new Promise((resolve, reject) => {
let r = database.connect();
r.then(conn => database.table('table').filter({username:username}))
.then(data => resolve(data))
.catch(err => reject(err));
});
}
module.exports = getUser;
And the test file, using mocha and chai.expect, which is could also be any other unit test module here:
let td = require('testdouble');
let expect = require('chai').expect;
const getUser = require('./some');
describe('some.js',()=>{
it('getUser',()=>{
const db = {};
const name = 'name';
db.connect = td.function();
db.table = td.function('table');
db.filter = td.function('filter');
td.when(db.connect()).thenResolve(db);
td.when(db.table('table')).thenReturn(db);
td.when(db.filter({username: name})).thenResolve('some user data');
return getUser(db, name)
.then(user=>{
expect(user).to.equal('some user data')
})
.catch(e=>assert(e))
})
})
So please let me know if any of these confuse you.