Unit Testing in GAS Part 5: Testing Objects and Arrays

Published: 2020-01-14 03:44 |

Category: Code | Tags: code, google apps script, software, testing, tutorial, unit testing

If you're brand new to unit testing, start with the first post in this series to get caught up.

It's time to dive into deeper equality situations with objects and arrays. Every test we've written so far has used a non-strict comparison. In other words, we've only been checking value but not type. This is particularly important in JavaScript because of how it handles truthy and falsy values.

For instance, if you were to write a test checking the equality of 0 and undefined, what would you expect? They're different, right? If you want to try it yourself, you can write a quick test:

QUnit.test('truthy and falsy values', function() {
    equal(0, undefined, 'both are falsy values, but unequal types') // pass
    deepEqual(0, undefined, 'both are falsy values, and unequal types') // fail

QUnit passes the first test because both 0 and undefined are falsy - the values are the same, but the type is different. Using equal as the assertion only checks against the value of the actual and expected arguments. This is where deepEqual helps. Instead of checking values only, deepEqual performs a strict check of both the value and type of the arguments.

Objects and Arrays

We have only looked at simple values - numbers and strings. In this post, we'll look at using deepEqual and propEqual to test objects and arrays. Rather than jumping right into testing our Calcs class, let's start with two simpler examples. Start by adding this to your tests.gs file:

// function calcTests() { ... }

// Create a new test wrapper to keep things neat
function objectTests() {
    QUnit.test('Object and array basics', function() {
        var array = [1,2,3,4];
        deepEqual(array, [1,2,3,4], 'the arrays are equal');

This is the first time we've defined a variable inside a Qunit.test instance. Each test is a function, so it can have block-scoped variables used in the test. These variables do not affect other functions in the wrapper. Eventually, we will be retrieving exisitng objects and arrays to test, but for now, we'll define them with each test as necessary.

Because we're defining a new wrapper, you need to go to config.gs and add objectTests() to the tests() wrapper for these new tests to run:

function tests() {
    console = Logger; // Match JS
    calcTests(); // Collection of tests on the Calcs class.
    objectTests(); // new tests for checking objects and arrays

This is personal preference, really...there is nothing saying you cannot include these checks in the calcTests wrapper we're using, but I find it helpful to break out tests into similar groups.

Reload the web app and you'll see a new line passing the array deepEqual check we just wrote. Let's do the same thing for an Object:

function objectTests() {
    // ... array check
    deepEqual({a: "hello", b: "world"}, {a: "hello", b: "world"}, 'These objects are equivalent');

This test will also pass because the objects have strict equality with one another. deepEqual is recursive, meaning it will check for equality even within nested objects:

function objectTests() {
// ... array check
// ... shallow object check
        a: "hello",
        b: "world",
        c: {
            aa: "foo",
            bb: "bar"
    }, {
        a: "hello",
        b: "world",
        c: {
            aa: "foo",
            bb: "bar"
    }, 'Nested objects can be tested, too');

Checking Constructed Objects

Checking object constructors is complicated. You cannot just define a matching object in the function because deepEqual checks the constructor along with the value. Rather than testing the entire object, it is better to check each part of the object.

This follows with the unit testing philosophy - test the smallest possible pieces of your code. If you want to test the structure of the object, we can assign a variable to an object with the desired properties and test our Calcs object against it with propEqual.

To help with flow control, I've added an init() method Calcs which will return the entire object. It doesn't matter a whole not right now, but it will in future posts.

var Calcs = (function() {
    const init = function() {
        return this;
    // rest of Calcs

From now on, when we need to instantiate Calcs, we'll use Calcs.init().

To test obect properties, let's add a variable with a known structure to use as our expected value. Then, we'll call Calcs.init() to get the full object back to compare properties.

function objectTests() {
    // ... array, shallow, and deep object checks
    // Model the structure of the Calcs object
    var testCalcsClass = {
      init: function() {},
      name: "calculation methods",
      about: function() {},
      author: function() {},
      add: function(a, b) {},
      isNumber: function(val) {},
      addArray: function(arr, int) {},
    // .. array, object checks
    propEqual(Calcs.init(), testCalcsClass, 'The constructed object has the expected structure.');

propEqual returns true because the properties of both are the same. Calling deepEqual will cause a failure because it checks the properties and the object constructor. Our expected value wasn't created with a constructor like the actual and the test will fail.

Why might this type of check be important?

If your object returns the wrong type of value, propEqual will fail. For example, changing init to a string value in your expected object will fail when compared with Calcs.init() because it's expecting a function, not a string.

Using propEqual on your classes can help prevent type errors down the line by ensuring each property matches the expected type. This kind of check, where you specify an expected structure, is called mocking and we'll look at that in a future post.

Testing Returned Values

What about functions or methods that return structured data? We can use deepEqual to check the returned values. We're going to add a method to Calcs which accepts an array and integer and returns an array with each value increased by the specified amount. Here's the test we'll run:

QUnit.test('Test array calculations', function() {
    equal(Calcs.addArray(2, 2), false, 'Param 1 is not an array');
    equal(Calcs.addArray([1,2,3], 'dog'), false, 'Param 2 is a string');
    deepEqual(Calcs.addArray([1, 2, 3], 2), [3, 4, 5], 'The returned array is correct');

Our test defines three checks that need to pass:

  1. The first parameter is an array,
  2. the second parameter is a number,
  3. and the returned array is equal to the expected value.

Our method needs to accept an array and a number to add to each value in the array. We should get a new array back with the updated values.

const addArray = function(arr, int) {
    // Check the params
    if (!Array.isArray(arr)) { return false }
    if (typeof int !== 'number') { return false }

    var addArr = arr.map(function(val) { return val + int })

    return addArr;

return {
    // rest of return
    addArray: addArray

If you reload your web app, all tests should pass. This could also be extended with throws to check for custom error messages like we did back in part 4.

Put it into practice

It's easy to get sucked into thinking you need to check for exact data, particularly with Objects and Arrays. With unit testing, remember that you're checking that a piece of your code does what it's designed to do with any data. Running tests on generic structures gives you a clear idea of what any individual part of your application does. Use propEqual to test mocked objects for structure.


  • equal does a soft comparison (==) and deepEqual uses a strict check (===).
  • deepEqual also checks constructor values for Objects.
  • propEqual compares Object properties (structure) without considering the constructor.

Comments are always open. You can get in touch by sending me an email at brian@ohheybrian.com