Override

The as-simple-as-possible-but-not-simpler stubbing library.

Override is the essence of the stubbing concept: it takes an object, a hash of methods/results, and proceeds to rewrite each method in the object. It can be used as a stubbing strategy in most cases, and I'd say that cases that don't fit this pattern have a very bad code smell, because are either dealing with internals or with side effects.

require 'override'

include Override

user = User.spawn
override(user, :name => "Foobar", :email => "foobar@example.org")
override(User, :find => user)

Or alternatively:

override(User, :find => override(User.spawn, :name => "Foobar, :email => "foobar@example.org"))

You can also send lambdas that will become the body of the redefined method:

user = User.spawn :name => "Foobar"
override(User, :find => lambda { |id| raise ArgumentError unless id == 1; user })

And then, in your tests:

assert_raise ArgumentError do
  User.find(2)
end

assert_nothing_raised do
  User.find(1)
end

assert_equal "Foobar", User.find(1).name

In case you don't know what spawn means, check my library Spawn.

It is a common pattern to set expectations for method calls. You can do it with the expect function:

user = User.spawn :name => "Foobar"
expect(User, :find, :with => [:first, { :include => :friendships }], :return => user)

And then:

assert_equal "Foobar", User.find(:first, :include => :friendships).name

This kind of tests encourage a very fine grained development style. Testing side effects is possible with this and with many other libraries, but it's something that should be avoided as much as possible. Always keep in mind that a deterministic function is the easiest to test, so the less coupling there is in the system, the more reliable it becomes.

Note that this way of setting expectations doesn't count the number of calls received by the redefined method. The RSpec equivalent of User.should_receive(:find).with(:first, :include => :friendships) triggers an exception if the method is not called. While it is a handy feature, it encourages coupling and testing internals, so my advice would be to use it scarcely and to try to refactor your code so it doesn't follow this testing anti-pattern. Check the tests for more examples.

$ sudo gem install override

Thanks to Tim Goh for his advice of using a hash for rewriting multiple methods at once.

Copyright (c) 2009 Michel Martens

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