Jasmine JavaScript Testing - toBe vs toEqual Jasmine JavaScript Testing - toBe vs toEqual javascript javascript

Jasmine JavaScript Testing - toBe vs toEqual


For primitive types (e.g. numbers, booleans, strings, etc.), there is no difference between toBe and toEqual; either one will work for 5, true, or "the cake is a lie".

To understand the difference between toBe and toEqual, let's imagine three objects.

var a = { bar: 'baz' },    b = { foo: a },    c = { foo: a };

Using a strict comparison (===), some things are "the same":

> b.foo.bar === c.foo.bartrue> b.foo.bar === a.bartrue> c.foo === b.footrue

But some things, even though they are "equal", are not "the same", since they represent objects that live in different locations in memory.

> b === cfalse

Jasmine's toBe matcher is nothing more than a wrapper for a strict equality comparison

expect(c.foo).toBe(b.foo)

is the same thing as

expect(c.foo === b.foo).toBe(true)

Don't just take my word for it; see the source code for toBe.

But b and c represent functionally equivalent objects; they both look like

{ foo: { bar: 'baz' } }

Wouldn't it be great if we could say that b and c are "equal" even if they don't represent the same object?

Enter toEqual, which checks "deep equality" (i.e. does a recursive search through the objects to determine whether the values for their keys are equivalent). Both of the following tests will pass:

expect(b).not.toBe(c);expect(b).toEqual(c);

Hope that helps clarify some things.


toBe() versus toEqual(): toEqual() checks equivalence. toBe(), on the other hand, makes sure that they're the exact same object.

I would say use toBe() when comparing values, and toEqual() when comparing objects.

When comparing primitive types, toEqual() and toBe() will yield the same result. When comparing objects, toBe() is a stricter comparison, and if it is not the exact same object in memory this will return false. So unless you want to make sure it's the exact same object in memory, use toEqual() for comparing objects.

Check this link out for more info : http://evanhahn.com/how-do-i-jasmine/

Now when looking at the difference between toBe() and toEqual() when it comes to numbers, there shouldn't be any difference so long as your comparison is correct. 5 will always be equivalent to 5.

A nice place to play around with this to see different outcomes is here

Update

An easy way to look at toBe() and toEqual() is to understand what exactly they do in JavaScript. According to Jasmine API, found here:

toEqual() works for simple literals and variables, and should work for objects

toBe() compares with ===

Essentially what that is saying is toEqual() and toBe() are similar Javascripts === operator except toBe() is also checking to make sure it is the exact same object, in that for the example below objectOne === objectTwo //returns false as well. However, toEqual() will return true in that situation.

Now, you can at least understand why when given:

var objectOne = {    propertyOne: str,    propertyTwo: num    }var objectTwo = {    propertyOne: str,    propertyTwo: num    }

expect(objectOne).toBe(objectTwo); //returns false

That is because, as stated in this answer to a different, but similar question, the === operator actually means that both operands reference the same object, or in case of value types, have the same value.


To quote the jasmine github project,

expect(x).toEqual(y); compares objects or primitives x and y and passes if they are equivalent

expect(x).toBe(y); compares objects or primitives x and y and passes if they are the same object