Just a quick note:

If you are testing a module which you include in multiple controllers you need to describe the controller name you are testing, not the module name or you end up with the stack trace below

Failure/Error: Unable to find matching line from backtrace
NoMethodError:
undefined method `original_path_set' for nil:NilClass
  /Users/mark/.rvm/gems/ruby-1.9.3-p0/gems/rspec-rails-2.8.1/lib/rspec/rails/view_rendering.rb:113:in `block (2 levels) in <module:ViewRendering>'
  /Users/mark/.rvm/gems/ruby-1.9.3-p0/gems/rspec-core-2.8.0/lib/rspec/core/example_group.rb:435:in `instance_eval'
  /Users/mark/.rvm/gems/ruby-1.9.3-p0/gems/rspec-core-2.8.0/lib/rspec/core/example_group.rb:435:in `instance_eval_with_rescue'
  /Users/mark/.rvm/gems/ruby-1.9.3-p0/gems/rspec-core-2.8.0/lib/rspec/core/hooks.rb:45:in `run_in'
  /Users/mark/.rvm/gems/ruby-1.9.3-p0/gems/rspec-core-2.8.0/lib/rspec/core/hooks.rb:80:in `block in run_all'
  /Users/mark/.rvm/gems/ruby-1.9.3-p0/gems/rspec-core-2.8.0/lib/rspec/core/hooks.rb:80:in `each'
  /Users/mark/.rvm/gems/ruby-1.9.3-p0/gems/rspec-core-2.8.0/lib/rspec/core/hooks.rb:80:in `run_all'
  /Users/mark/.rvm/gems/ruby-1.9.3-p0/gems/rspec-core-2.8.0/lib/rspec/core/hooks.rb:368:in `run_hook'
  /Users/mark/.rvm/gems/ruby-1.9.3-p0/gems/rspec-core-2.8.0/lib/rspec/core/example_group.rb:297:in `block in run_after_each_hooks'
  /Users/mark/.rvm/gems/ruby-1.9.3-p0/gems/rspec-core-2.8.0/lib/rspec/core/example_group.rb:297:in `each'
  /Users/mark/.rvm/gems/ruby-1.9.3-p0/gems/rspec-core-2.8.0/lib/rspec/core/example_group.rb:297:in `run_after_each_hooks'
  /Users/mark/.rvm/gems/ruby-1.9.3-p0/gems/rspec-core-2.8.0/lib/rspec/core/example.rb:221:in `run_after_each'
  /Users/mark/.rvm/gems/ruby-1.9.3-p0/gems/rspec-core-2.8.0/lib/rspec/core/example.rb:86:in `block in run'
class FakeTestController < ApplicationController
  include YourModuleName

  def update
    your_module_method_under_test
  end
end

#rather than
describe YourModule do
  describe "#your_module_method_under_test"
  #...
end

#do this instead:
describe FakeTestController
  describe "#your_module_method_under_test"
  #...
end

Original gist