Testing Bluebird promises with Mocha | The N00b Developer

So I have a node.js application that contains the getAccountInfoFromToken function below, and I want to test it with Mocha. This function has been gutted and the account details are embedded now instead of called in to make the example clearer.

Promise = require('bluebird'),
getAccountInfoFromToken: function(token) {
    return new Promise(function(resolve, reject){
        // Get Account details
        var sample_return = {
            "accounts": [
                {
                    "account_id": 1725389
                }
            ],
        };
        var accounts = sample_return["accounts"];
        if (accounts.length > 0) {
            resolve(accounts);
        } else {
            reject('No Accounts');
        }
    });
}

So initially I took a very naive approach to the test because I wasn’t clear on how javascript compared arrays. So I had the test you see below.

"use strict";

describe("token_vending_machine", function () {
    var tvm = require("../src/server"),
        sinon = require("sinon"),
        assert = require("assert"),
        expected_token_return = [
            {"account_id": 1725389}
        ];

    describe("#getAccountInfoFromToken()", function () {
        it("should return the right details when called with a token", function () {
            tvm.getAccountInfoFromToken("test").then(function (data) {
                assert.equal(data, expected_token_return);
            })
        });
    });
});

However Mocha would report that as a pass but then I got an error from Bluebird about a possibly unhandled AssertionError… like you see in the output below.

token_vending_machine
    #getAccountInfoFromToken()
    ✓ should return the right details when called with a token
Possibly unhandled AssertionError: [{"account_id":1725389}] == [{"account_id":1725389}]
    at /Users/jmyers/dev/token_vending_machine/test/tvm.js:40:24
    at tryCatch1 (/Users/jmyers/dev/token_vending_machine/node_modules/bluebird/js/main/util.js:43:21)
    at Promise$_callHandler [as _callHandler] (/Users/jmyers/dev/token_vending_machine/node_modules/bluebird/js/main/promise.js:627:13)
    at Promise$_settlePromiseFromHandler [as _settlePromiseFromHandler] (/Users/jmyers/dev/token_vending_machine/node_modules/bluebird/js/main/promise.js:641:18)
    at Promise$_settlePromiseAt [as _settlePromiseAt] (/Users/jmyers/dev/token_vending_machine/node_modules/bluebird/js/main/promise.js:804:14)
    at Promise$_settlePromises [as _settlePromises] (/Users/jmyers/dev/token_vending_machine/node_modules/bluebird/js/main/promise.js:938:14)
    at Async$_consumeFunctionBuffer [as _consumeFunctionBuffer] (/Users/jmyers/dev/token_vending_machine/node_modules/bluebird/js/main/async.js:75:12)
    at Async$consumeFunctionBuffer (/Users/jmyers/dev/token_vending_machine/node_modules/bluebird/js/main/async.js:38:14)
    at process._tickDomainCallback (node.js:463:13)


1 passing (8ms)

That possible assertion error is a real thing because I thought my test was passing when it wasn’t because Mocha wasn’t getting the information it needed. Next I tried to catch the error and throw it. So I edited the test like so…

    describe("#getAccountInfoFromToken()", function () {
        it("should return the right details when called with a token", function () {
            tvm.getAccountInfoFromToken("test").then(function (data) {
                assert.equal(data, expected_token_return);
            }).catch(function (err) {
                console.error(err);
            })
        });
    });

That lead to a timeout error, which actually made Mocha show the test as failing. It also logged what the actual error was. That output is below

token_vending_machine
    #getAccountInfoFromToken()
{ [AssertionError: [{"account_id":1725389}] == [{"account_id":1725389}]]
name: 'AssertionError',
actual: [ { account_id: 1725389 } ],
expected: [ { account_id: 1725389 } ],
operator: '==',
message: '[{"account_id":1725389}] == [{"account_id":1725389}]' }
    1) should return the right details when called with a token


0 passing (2s)
1 failing

1) token_vending_machine #getAccountInfoFromToken() should return the right details when called with a token:
    Error: timeout of 2000ms exceeded
    at null.<anonymous> (/Users/jmyers/dev/token_vending_machine/node_modules/mocha/lib/runnable.js:157:19)
    at Timer.listOnTimeout [as ontimeout] (timers.js:112:15)

Now I knew I needed to use a deepEqual to get the test to pass; however, I still didn’t wanna have to wait 2 seconds per test for my test to get marked as a failure. Enter Mocha’s done function which tells Mocha that the test is complete. It needs to be called after the assertion, and in the error handler in order to work properly. Here is the updated test.

describe("#getAccountInfoFromToken()", function () {
    it("should return the right details when called with a token", function (done) {
        tvm.getAccountInfoFromToken("test").then(function (data) {
            assert.equal(data, expected_token_return);
            done();
        }).catch(function (err) {
            done(err);
        });
    });
});

the clearer Mocha output:

token_vending_machine
    #getAccountInfoFromToken()
    1) should return the right details when called with a token


0 passing (6ms)
1 failing

1) token_vending_machine #getAccountInfoFromToken() should return the right details when called with a token:
    AssertionError: [{"account_id":1725389}] == [{"account_id":1725389}]
    at /Users/jmyers/dev/token_vending_machine/test/tvm.js:35:24
    at tryCatch1 (/Users/jmyers/dev/token_vending_machine/node_modules/bluebird/js/main/util.js:43:21)
    at Promise$_callHandler [as _callHandler] (/Users/jmyers/dev/token_vending_machine/node_modules/bluebird/js/main/promise.js:627:13)
    at Promise$_settlePromiseFromHandler [as _settlePromiseFromHandler] (/Users/jmyers/dev/token_vending_machine/node_modules/bluebird/js/main/promise.js:641:18)
    at Promise$_settlePromiseAt [as _settlePromiseAt] (/Users/jmyers/dev/token_vending_machine/node_modules/bluebird/js/main/promise.js:804:14)
    at Async$_consumeFunctionBuffer [as _consumeFunctionBuffer] (/Users/jmyers/dev/token_vending_machine/node_modules/bluebird/js/main/async.js:75:12)
    at Async$consumeFunctionBuffer (/Users/jmyers/dev/token_vending_machine/node_modules/bluebird/js/main/async.js:38:14)
    at process._tickDomainCallback (node.js:463:13)

Now to actually make the two arrays compare properly and getting a passing test. All that we need to do is to do a deepEqual instead of an equal.

describe("#getAccountInfoFromToken()", function () {
    it("should return the right details when called with a token", function (done) {
        tvm.getAccountInfoFromToken("test").then(function (data) {
            assert.deepEqual(data, expected_token_return);
            done();
        }).catch(function (err) {
            done(err);
        });
    });
});

And our happy Mocha output:

token_vending_machine
  #getAccountInfoFromToken()
    ✓ should return the right details when called with a token


1 passing (6ms)