DZone Snippets: mock code

Simple mock: override_method

MattScilipoti (Matt Scilipoti) — Mon, 18 Jun 2007 18:48:01 GMT

Note: ALL code samples in this post were hijacked from: http://www.karmiccoding.com/articles/2006/03/11/under-the-hood-with-ruby-partial-mock-objects-for-unit-testing



# Overrides the method +method_name+ in +obj+ with the passed block

def override_method(obj, method_name, &block)

  # Get the singleton class/eigenclass for 'obj'

  klass = class <

  # Undefine the old method (using 'send' since 'undef_method' is protected)

  klass.send(:undef_method, method_name)



  # Create the new method

  klass.send(:define_method, method_name, block)

end



# Just an example class

class Foo 

  def do_stuff

    "I'm okay!" 

  end

end



# Test code

list = []

5.times { list.push(Foo.new) }



# We override the method here!

override_method(list.first, :do_stuff) { "I'm NOT okay!" }



list.each_with_index { |f, i| puts "(#{i}) #{f.do_stuff}" }

Outputs:
(0) I'm NOT okay!
(1) I'm okay!
(2) I'm okay!
(3) I'm okay!
(4) I'm okay!

Partial Mock Object or mocking an instance of an object.

MattScilipoti (Matt Scilipoti) — Sun, 12 Mar 2006 09:33:38 GMT

From: http://www.karmiccoding.com/articles/2006/03/11/under-the-hood-with-ruby-partial-mock-objects-for-unit-testing

"What happens though, if you want to override a class in an instance of an object, and not all of its kind? Typically you would define a mock object, and create an instance of it. But, in Ruby there is an easier and faster way that doesn’t involve writing a different mock class for each different scenario – and it is made possible by the singleton class. This clever bit of ruby hackery lets you override the behaviour of a single instance of a class, creating what I’ve decided to call a partial mock object. To demonstrate, I’ve written a small method called override_method which will override the behaviour of the specified method in the passed object, like so:



# Overrides the method +method_name+ in +obj+ with the passed block

def override_method(obj, method_name, &block)

  # Get the singleton class/eigenclass for 'obj'

  klass = class <

  # Undefine the old method (using 'send' since 'undef_method' is protected)

  klass.send(:undef_method, method_name)



  # Create the new method

  klass.send(:define_method, method_name, block)

end



# Just an example class

class Foo 

  def do_stuff

    "I'm okay!" 

  end

end



# Test code

list = []

5.times { list.push(Foo.new) }



# We override the method here!

override_method(list.first, :do_stuff) { "I'm NOT okay!" }



list.each_with_index { |f, i| puts "(#{i}) #{f.do_stuff}" }



Outputs:

(0) I'm NOT okay!

(1) I'm okay!

(2) I'm okay!

(3) I'm okay!

(4) I'm okay!

As you can see, only the first object in the array’s behaviour has been changed – the rest have remained untouched. Because of this, you can embed these partial dynamic mock objects deeply into your code without the need to specially instantiate a mock object deep in your code, or writing a ‘clever mock’ to only trigger the determined behaviour in certain objects.

Where this code comes in really handy is when you need an object to raise a difficult to simulate exception (like a disk full error) on a certain method to test your error handling – simply call override_method and pass in a call to raise and voila! Dynamic partial mock objects on the fly!"

mocking ActiveRecord

technoweenie (Rick Olson) — Wed, 28 Sep 2005 06:48:08 GMT

A search didn't turn anything up, so I tried this:

ActiveRecord::Base.class_eval do

  alias_method :save, :valid?

  def self.columns() @columns ||= []; end

  

  def self.column(name, sql_type = nil, default = nil, null = true)

    columns << ActiveRecord::ConnectionAdapters::Column.new(name.to_s, default, sql_type, null)

  end

end

The mock model:

class User < ActiveRecord::Base

  validates_presence_of :login

  column :id,       :integer

  column :login,    :string

  column :password, :string

  column :active,   :boolean, true

end

This should provide a quick way to test validations and things like that...