What is describe() in Mocha

Question

I am trying to get my hands dirty with Mocha and here is the example I saw from documentation:

var assert = require("assert")
describe('Array', function(){
  describe('#indexOf()', function(){
    it('should return -1 when the value is not present', function(){
      assert.equal(-1, [1,2,3].indexOf(5));
      assert.equal(-1, [1,2,3].indexOf(0));
    })
  })
})

Most of the examples show the second describe statement

  describe('#indexOf()', function(){

starting with # in #indexOf(). What is the significance of this #? Why can this not be written simply as indexOf? Where can I get a fundamental understanding of how the describe works?

PS: I looked at the documentation at http://visionmedia.github.io/mocha/#interfaces but can't figure out how these came into picture and how are these interfaces processed.

Thx

That's jus a string, it means absolutely nothing. It's just like Array#indexOf(), basically indexOf is a function of the Array Class/Object — dcodesmith, Jan 25 '14 at 17:18
why do all people give answers without minimal research?, `#` does means something (instance method), and it's well established convention, I added my answer below. — Benja, Aug 02 '14 at 05:37
This is essentially a duplicate of http://stackoverflow.com/questions/19298118/what-is-the-role-of-describe-in-mocha#_=_ The answer there answers this as well. — Ian Michael Williams, Dec 02 '15 at 21:53

score 10 · Accepted Answer · answered Aug 02 '14 at 05:36

the bdd syntax of mocha is a inspired in ruby's RSpec, therefore you'd find the best tips for mocha's conventions searching for RSpec, here's a good place to start:

http://betterspecs.org/

In particular the # is mentioned there:

For instance, use the Ruby documentation convention of . (or ::) when referring to a class method's name and # when referring to an instance method's name.

score 1 · Answer 2 · answered Jan 25 '14 at 20:13

Looking at the source code of Mocha, I don't see it doing anything significant with a # appearing in the first parameter of describe.

This being said, in some documentation systems for JavaScript (for instance, jsdoc), the use of a # indicates that what follows belongs to an object instance, rather than to the object's class. So Foo#bar would be something you could call like this:

var foo = new Foo();
foo.bar(...);

Not like this:

Foo.bar(...)

The latter would be represented as Foo.bar. So it would make sense in a test suite to use the same kind of notation to distinguish whether the methods being tested belong to instances or classes.

score -1 · Answer 3 · answered Jan 31 '14 at 20:25

starting with # in #indexOf(). What is the significance of this #?

None. Some people think that it looks better.

Where can I get a fundamental understanding of how the describe works?

It's basically a way to group your tests together and run before/after for a group of tests.

You'll know when you need it, and if you're asking this question, you can safely ignore all describe's and write tests without them.

What is describe() in Mocha

3 Answers3

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