Mocha Quickstart

Posted by James Mead Fri, 01 Sep 2006 14:07:00 GMT

I really must get round to writing some better documentation for Mocha, but in the meantime here’s a quickstart guide1.

Mocha adds a couple of new methods to all objects and classes – expects which sets up auto-verified expectations and stubs which stubs the method allowing any number of calls.

Both the expects and stubs methods actually return an expectation object. Relevant methods on an expectation are: at_least, at_least_once, never, raises, returns, times, with, yields which are hopefully fairly self-explanatory. If not there are some clues here

Mocking a class method 
  product = Product.new
  Product.expects(:find).with(1).returns(product)
  assert_equal product, Product.find(1)
Mocking an instance method on a real object 
  product = Product.new
  product.expects(:save).returns(true)
  assert product.save
Stubbing instance methods on real object 
  prices = [stub(:pence => 1000), stub(:pence => 2000)]
  product = Product.new
  product.stubs(:prices).returns(prices)
  assert_equal [1000, 2000], product.prices.collect {|p| p.pence}
Stubbing an instance method on all instances of a class 
  Product.any_instance.stubs(:name).returns('stubbed_name')
  product = Product.new
  assert_equal 'stubbed_name', product.name
Traditional mocking 
  object = mock()
  object.expects(:expected_method).with(:p1, :p2).returns(:result)
  assert_equal :result, object.expected_method(:p1, :p2)
Shortcuts 
  object = stub(:method1 => :result1, :method2 => :result2)
  assert_equal :result1, object.method1
  assert_equal :result2, object.method2

1 I wrote these examples without checking them, so there may be some typos.

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Comments

  1. Jordan Arentsen said 51 days later:

    Hi,

    First of all, let me say, Mocha looks awesome and I’m really looking forward to using it (I’m a TDD newb you might say). However, when I tried to start using it on a Rails app, I encountered an error. It was something along the lines of “User object doesn’t have expects method”. I know I required it above the test case and also tried including it in the test_helper file (I installed it as a gem). Do you have any idea what I could be doing wrong?

  2. James Mead said 51 days later:

    Have you required ‘stubba’ as well as ‘mocha’?

    The latest svn HEAD does away with the distinction between ‘mocha’ & ‘stubba’, but the latest gem (mocha-0.3.2) is a bit out-of-date and you need to require both.

    You need ‘stubba’ if you need to do something like this…

      user = User.new
  user.expects(:login).returns('bilbo')

    or…

      User.expects(:authenticate).returns(false)

    Please use the mailing list for any other queries – thanks.

  3. Jordan Arentsen said 51 days later:

    Thanks James. I’ll use the mailing list next time.

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