with_modules_unavailable and some Module helpers

I've been trying to test a new Rails plugin (stay tuned!), and I've found that I need to have certain Modules unavailable. This is useful when you need to test that missing Modules will raise errors or if you have behavior conditional on what gems are installed.

I wanted something like:

...
with_modules_unavailable(Foo, Bar::Baz::Goo) do
  test stuff
end

To get this working, just put the following in your test_helper.rb (this version requires Inflector):

Module.class_eval do
  
  def defining_module
    chain = self.to_s.split(/\:\:/)
    chain.pop
    if chain.empty?
      Object
    else
      chain.join('::').constantize
    end
  end
  
  def simple_name
    self.to_s.split(/\:\:/).pop
  end
  
end

Test::Unit::TestCase.class_eval do

  def with_modules_unavailable(*mods, &block)
    Thread.exclusive do
      mods.each do |mod|
        mod.defining_module.send :remove_const, mod.simple_name.to_sym
      end
      yield block
      mods.reverse.each do |mod|
        mod.defining_module.send :const_set, mod.simple_name.to_sym, mod
      end
    end
  end
  
end

You can test that it works with:

def test_with_modules_unavailable
  with_modules_unavailable(ActiveRecord::Base) do
    assert_raise(NameError) { ::ActiveRecord::Base.class_eval { } }
  end
  assert_nothing_raised { ::ActiveRecord::Base.class_eval { } }
end