From: Robert Klemme <bob.news@...>
Date: 2005-04-14T17:49:36+09:00
Subject: Re: Mocking out a class object


"Avdi Grimm" <Avdi_B_Grimm@raytheon.com> schrieb im Newsbeitrag
news:ur7hep6w5.fsf@raytheon.com...
>
> Okay, I'm trying to mock up a class object.  It needs to do two
> things:
>
> 1. Respond to #new with a object *I* provide, rather than a new
>    instance of the class; and
> 2. Contain a constant, such that code containing 'MyMockClass::FOO'
>    will work.
>
> I can think of a naive implementation:
>
>     class MyMockClass
>         FOO="some value"
>         def self.set_instance(inst)
>             @instance=inst
>         end
>         def self.new(*)
>             return @instance
>         end
>     end
>
> I'm wondering, though, is there a way to do this inline with
> metaprogramming, and avoid defining the set_instance method?  I've
> tried something like this:
>
>     my_instance=...
>
>     Class.new :MyMockClass {
>         const_set :FOO, "some value"
>         define_method(:new) do |*|
>             return my_instance
>         end
>     }
>
> But that doesn't work, because the define_method is creating an
> instance method, not a class method.  I've also tried to use a regular
> old object, instead of a class object, but then the constant (FOO)
> doesn't work.  Any ideas?

You don't really need to make it so complicated IMHO:

class MockClass
  def initialize(obj) @obj = obj end
  def new() @obj end
end

>> MockClass::Foo = MockClass.new "foo"
=> #<MockClass:0x10189e38 @obj="foo">
>> MockClass::Foo.new
=> "foo"
>> MockClass::Foo.new.object_id
=> 135024424
>> MockClass::Foo.new.object_id
=> 135024424
>> MockClass::Foo.new.object_id
=> 135024424
>> MockClass::Foo.new.object_id
=> 135024424

Alternative

class MockClass
  def initialize(sym, obj)
    @obj = obj
    self.class.const_set sym, self
  end
  def new() @obj end
end

>> MockClass.new :Foo, "foo"
=> #<MockClass:0x101863e8 @obj="foo">
>> MockClass::Foo.new
=> "foo"
>> MockClass::Foo.new.object_id
=> 135016960
>> MockClass::Foo.new.object_id
=> 135016960
>> MockClass::Foo.new.object_id
=> 135016960
>> MockClass::Foo.new.object_id
=> 135016960


Kind regards

    robert