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Underscore Matchers for Jasmine

UnderscoreMatchersForJasmine adds a series of matchers for Jasmine-based JavaScript/Coffeescript testing based on Underscore methods, the Backbone library. Some handy JS expectations are thrown in as well that are helpful when testing your model objects (whether you use Backbone or not). Example:

expect(snafu).toInclude('s', 'n', 'a')

// if snafu is an array, this is equivalent to:
  _(snafu).include('s') && _(snafu).include('n') && _(snafu).include('a')

// if snafu is a Backbone.js collection, this is equivalent to:
  snafu.include('s') && snafu.include('n') && snafu.include('a')

That makes your tests easy to read, for example:

$ ->
  describe 'States and StateMachines', ->

    it 'should associate states with a state machine and the state machine with its states', ->
      engine_status = new StateMachine()
      running = engine_status.new_state()
      idling = engine_status.new_state()

      expect(engine_status.states()).toInclude(running, idling)

    it 'should generate states with rpm', ->
      engine_status = new StateMachine()
      running = engine_status.new_state()


The defining characteristic of UnderscoreMatchersForJasmine is its transparent support for Backbone. Expectations like .toInclude and .toHave work with standard JavaScript objects and also with Backbone collections and models transparently. For example, .toHave:

foo =
    bar: 'bash'

  # => false
  # => true

_.has(foo, 'bar')
  # => false
_.has(foo, 'attributes')
  # => true


When you have a standard JS object, the toHave expectation mirrors .hasOwnProperty or _.has

fooModel = new Backbone.Model
  bar: 'bash'

  # => false
  # => true

_.has(foo, 'bar')
  # => false
_.has(foo, 'attributes')
  # => true


When you have a Backbone model, the toHave expectation mirrors .has from Backbone: It tests whether the model has an attribute. This is nearly always what you want.

Is it any good?


Why is it any good?

Let's take it point by point:

  1. Underscore is a utility-belt library for JavaScript. Backbone.js is a lightweight MVC library for JavaScript.
  2. Jasmine is a Test-Driven Development testing framework for JavaScript. You can run tests in a pretty browser window, you can run tests on the command line with Node.js, you can run tests in the console. If you are writing JavaScript and/or Coffeescript, you should be using Jasmine.
  3. If you are using Underscore or Backbone and you are using Jasmine, your tests will be cleaner and more readable with these matchers for the same reason that your code is cleaner and more readable with Underscore and Backbone.

Which matchers are included?

Read the code in Coffeescript or JavaScript.

Or, here's the "tl;dr:"

# collections:

expect([...]).toBeEmpty()         or expect(new Backbone.Collection(...)).toBeEmpty()
expect([...]).toInclude(foo, bar) or expect(new Backbone.Collection(...)).toInclude(foo, bar)
expect([...]).toIncludeAny(blitz) or expect(new Backbone.Collection(...)).toIncludeAny(blitz)
expect([...]).toBeCompact()       or expect(new Backbone.Collection(...)).toBeCompact()
expect([...]).toBeUnique()        or expect(new Backbone.Collection(...)).toBeUnique()

# object methods

expect(foo).toRespondTo('push', 'pop')
expect(foo).toRespondToAny('push', 'isEmpty')

# object properties

expect(foo).toHave('length', 'arity')
expect(foo).toHaveAny('length', 'size')

# model properties

var Sidebar = Backbone.Model.extend({
  promptColor: function() {
    var cssColor = prompt("Please enter a CSS color:");
    this.set({color: cssColor});

myBar = new Sidebar();

expect(myBar).not.toHave('color'); # we haven't set a color

myBar.set({color: ...});

expect(myBar).toHave('color'); # we haven't set a color

# OO and is-a (all synonymous)

expect(new Foo()).toBeAnInstanceOf(Foo)
expect(new Foo()).toBeA(Foo)
expect(new Foo()).toBeAn(Foo)

Are there any more?

This is what I happen to need right now for my actual code. As I write more matchers, I'll add them. So, if you're interested, watch the library. I suppose I could go through and make a matcher for every function in Underscore, but I'd rather let it grow organically. If there's a matcher you need that isn't here, well, we're all in the same boat:

  • If you're a passenger, send me a message describing the matcher you want. If it seems useful, I'll add it.
  • If you're a sailor, fork this project, add the matcher, and send me a pull request.
  • If you're the captain of your own ship, and you've already written some matchers like this, run up some signal flags and I'll include links to your project right here.
  • And if you're a pirate, take this code and/or just the idea and make your own library. I'm cool with that.

I use jasmine-node. Can I install it with npm?


npm install UnderscoreMatchersForJasmine

Can I install it in other kinds of projects?

If you're using Coffeescript, put in your project. If you're using plain JavaScript, it should therefore follow that you want to put underscore_matchers.js in your project. You can also put or underscore_matchers_spec.js in your project if you want to see these matchers test themselves. It's also handy documentation for how the matchers behave!

Is it free?


Other Random Observations

Who's Using This?

I am.

Is there a gem?

No. This is a Coffeescript and JavaScript include file, not a ruby library. Coffeescript and JavaScript files work everywhere, and you can read the source any time you want.

Any gotchas?

Some matchers, such as toInclude(...) and toRespondTo(...) can take multiple arguments. When they do, they have "all" semantics. For example:

expect([1,2,3,4,5]).toRespondTo('push', 'pop')
  // => succeeds because arrays respond to .push and .pop

   // => fails because 6 is not included.

Now what if you want to test the opposite?

  // succeeds because it doesn't include 2, 3, 4, 5, AND 6.

If that's what you want, fine. But if what you really want is to test whether it doesn't include ANY of the arguments, you need a slightly different matcher:

expect([1,2,3,4,5]).toRespondToAny('push', 'select_sql', 'diagonalize')
  // => succeeds because arrays respond to at least one of the three methods given

  //  => succeeds because it includes at least one of the arguments

The opposite of an "any" matcher is a "none" matcher:

expect([1,2,3,4,5]).not.toIncludeAny(3, 6, 9)
  //  => fails because [1,2,3,4,5] includes a 3

expect([1,2,3,4,5]).not.toIncludeAny(6, 9, 12)
  //  => succeeds because [1,2,3,4,5] does not include ANY of the aarguments

Is this just for underscore stuff?

No. I also sneak in some Backbone stuff here and there, but the code works just fine even if you don't use Backbone.js. For example:

$ ->
  describe 'States', ->
    it 'should permit cards to be added and removed', ->
      state = new State()
      card = new Card()

toBeEmpty is more than just a wrapper for _.isEmpty:

).toBeTruthy() // => succeeds

  _(new Backbone.Collection()).isEmpty()
).toBeTruthy() // => fails, wtf!?

  // => succeeds

expect(new Backbone.Collection()).toBeEmpty()
  // => succeeds

The same goes for collection tests like .toInclude. You can pass it a backbone collection or an array as you see fit. If you don't want that behaviour, Jasmine includes a contains() matcher that expects an array.

post scriptum

I'm writing a book called CoffeeScript Ristretto. Check it out!