how can I test fail error function with chai and mocha - node.js

Question

Hello guys i'm newbie with testing
I'm using socket.io and I want to simulate throwing error by my function when something happens on the insertion.
socket.on('request', function(request) {
bookingService.addBooking(request)
.then(function (booking) {
winston.info('Client Order saved');
io.emit('order to driver', {user: request[2], random : request[3]});
})
.catch(function (err) {
winston.error(' Client error on save order ==> '+err);
});
});
addBooking
function addBooking(msgParam) {
var deferred = Q.defer();
db.booking.insert(
{ user : msgParam[2],
adress : msgParam[0],
random : msgParam[3],
driver : [],
isTaken : false,
isDone : false,
declineNbr : 0 ,
createdOn : msgParam[1],
createdBy : msgParam[2],
updatedOn : null,
updatedBy : []},
function (err, doc) {
if (err) deferred.reject(err.name + ': ' + err.message);
deferred.resolve();
});
return deferred.promise;
}
I tried to just test the addBokking function
it('should throw error if something wrong happend on adding new order ', function(done){
(bookingService.addBooking(request)).should.throw()
done();
});
but I get this error
AssertionError: expected { state: 'pending' } to be a function

Answer 1

You can use the following syntax with chai:
it("throw test", () => {
expect(()=>{myMethodThatWillThrowError()}).to.throw();
});
For promises, you can use the following pattern:
it("should throw on unsuccessfull request", (done: MochaDone) => {
repo.patch({
idOrPath: "Root/Sites/Default_Site",
content: ConstantContent.PORTAL_ROOT,
}).then(() => {
done("Should throw"); // The test will fail with the "Should throw" error
}).catch(() => {
done(); // The test will report success
});
});

Answer 2

You are checking the promise and not the result
This error:
AssertionError: expected { state: 'pending' } to be a function
... means you are checking the promise returned from the addBooking function and not the resolved/rejected result of the promise.
With chai-as-promised you can do that easily!
With chai-as-promised these should work for example (from the documentation):
return promise.should.be.rejected;
return promise.should.be.rejectedWith(Error); // other variants of Chai's `throw` assertion work too.
or in your specific case (after installing and connecting chai-as-promised), this should work:
(bookingService.addBooking(request)).should.be.rejected
(maybe should.throw() will work with chai-as-promised too, I'm less familiar with it)
Check it out here: chai-as-promised