FAQ: Write Expressive Tests - assert.deepEqual I

This community-built FAQ covers the “assert.deepEqual I” exercise from the lesson “Write Expressive Tests”.

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Web Development

Learn JavaScript Unit Testing

FAQs on the exercise assert.deepEqual I

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Hi, could someone please clarify where does sum.results comes? It makes no sense to me.

let expected = {a: 3, b: 4, result: 7};
		let sum = {a: 3, b: 4};

    // Exercise
		**sum.result** = sum.a + sum.b;

    // Verify
    assert.deepEqual(sum, expected);
1 Like

sum.result = sum.a + sum.b; adds result property to sum object. So now you can assert your objects are the same.

5 Likes

Thanks, it would have thought it needed the .push() method to add it into the sum object, but I must be confusing it with an array. Seems to work just fine like this.

Just for fun, I tried another one:

describe('+', () => {
  it('returns the sum of two values', () => {
    // Setup
		let expected = {a: 3, b: 4, result: 7, substract: -1};
		let sum = {a: 3, b: 4};

    // Exercise
		sum.result = sum.a + sum.b;
		sum.substract = sum.a - sum.b;

    // Verify
    assert.deepEqual(sum, expected);
  });
});

Test passed: indeed, properties can be added to objects seamlessly using this method.

yea, if we look at some documentation:

Working with objects - JavaScript | MDN

we can see that objects are also associative arrays. so we could also add keys using:

sum['result'] = sum.a + sum.b;
1 Like

What is the difference between assert.equal() and assert.deepEqual()?

In the exercise before this one, it states this:

  • assert.equal() performs a == comparison.

Then for the assert.deepEqual() it states this:

  • This method compares the values of each object using loose ( == ) equality.

So what exactly is the difference between these two?

Its explained in the exercise:

using .equal to compare strings and so forth is fine. But won’t work for objects. Which is why we use deepEqual, which very likely uses a loop to compare all the items within the object

1 Like

Sorry I’m late to the party. This goes back to the reference over value section we had gone over. Objects are referenced by location. So with both objects having the same key value pairs they are considered different in nature. It still seems weird, but the deep equal does go deep into the object itself to extract the actual value to compare against. Whereas the .equal and .strictEqual are comparing the object, it will always return Falsey because they are different objects within memory.