JavaScript Testing with Jasmine

Chapter 4. Matchers in Depth

There are a lot of useful matchers that come with Jasmine. Later in this section, you’ll also see how to build your own.

Equality: toEqual

Perhaps the simplest matcher in Jasmine is toEqual. It simply checks if two things are equal (and not necessarily the same exact object, as you’ll see in Chapter 5).

The following expect functions will pass:

expect(true).toEqual(true);
expect([1, 2, 3]).toEqual([1, 2, 3]);
expect({}).toEqual({});

Here are some examples of toEqual that will fail:

expect(5).toEqual(12);
expect([1, 2, 3, 4]).toEqual([1, 2, 3]);
expect(true).toEqual(100);

Keep in mind that this is different from the toBe matcher. The subtle difference is noted next.

Identity: toBe

At first, the toBe matcher looks a lot like the toEqual matcher, but it’s not exactly the same. toBe checks if two things are the same object, not just if they are equivalent.

Here’s an example spec that illustrates the difference between toEqual and toBe:

var spot = { species: "Border Collie" };
var cosmo = { species: "Border Collie" };
expect(spot).toEqual(cosmo);  // success; equivalent
expect(spot).toBe(cosmo);     // failure; not the same object
expect(spot).toBe(spot);      // success; the same object

We see that, although spot and cosmo look really similar and are equal, they aren’t the same object. Because of that, they evaluate as equal, not the same.

The same is also true for arrays:

var arr = [1, 2, 3]; expect(arr).toEqual([1, 2, 3]); // success; equivalent expect(arr).toBe([1, 2, 3]); // ...