Gemfile

source :rubygems

gem 'rspec'
gem 'rspec-fire', git: 'git://github.com/myronmarston/rspec-fire.git', ref: '48d85c5545f338517c400b464b4ab8a4b9daca4a'
gem 'sinatra'

Gemfile.lock

GIT
  remote: git://github.com/myronmarston/rspec-fire.git
  revision: 48d85c5545f338517c400b464b4ab8a4b9daca4a
  ref: 48d85c5545f338517c400b464b4ab8a4b9daca4a
  specs:
    rspec-fire (0.2.2)

GEM
  remote: http://rubygems.org/
  specs:
    diff-lcs (1.1.3)
    rack (1.4.1)
    rack-protection (1.2.0)
      rack
    rspec (2.8.0)
      rspec-core (~> 2.8.0)
      rspec-expectations (~> 2.8.0)
      rspec-mocks (~> 2.8.0)
    rspec-core (2.8.0)
    rspec-expectations (2.8.0)
      diff-lcs (~> 1.1.2)
    rspec-mocks (2.8.0)
    sinatra (1.3.2)
      rack (~> 1.3, >= 1.3.6)
      rack-protection (~> 1.2)
      tilt (~> 1.3, >= 1.3.3)
    tilt (1.3.3)

PLATFORMS
  ruby

DEPENDENCIES
  rspec
  rspec-fire!
  sinatra

issue_spec.rb

module ShardManager
  extend self

  def use(host, database)
    db = Object.new
    yield db
  end
end

class Projects
  def self.for_user(user_id)
    ShardManager.use("localhost", "db_for_user_#{user_id}") do |db|
      db[:projects].all
    end
  end
end

require 'rspec/fire'

describe Projects, ".for_user" do
  include RSpec::Fire

  it 'queries the correct shard' do
    db = { projects: stub(all: %w[ project1 project2 ]) }
    shard_manager = fire_replaced_class_double("ShardManager")
    shard_manager.should_receive(:use).
      with("localhost", "db_for_user_17").and_yield(db)

    Projects.for_user(17).should eq(%w[ project1 project2 ])
  end
end

output

➜  rspec_mocks_issue_117 git:(master) ✗ ruby --version                  
ruby 1.9.3p125 (2012-02-16 revision 34643) [x86_64-darwin10.8.0]
➜  rspec_mocks_issue_117 git:(master) ✗ be rspec issue_spec.rb 
.

Finished in 0.00144 seconds
1 example, 0 failures
➜  rspec_mocks_issue_117 git:(master) ✗ be rspec issue_spec.rb -rsinatra
F

Failures:

  1) Projects.for_user queries the correct shard
     Failure/Error: ShardManager.use("localhost", "db_for_user_#{user_id}") do |db|
     NoMethodError:
       private method `use' called for ShardManager (fire double):Module
     # ./issue_spec.rb:12:in `for_user'
     # ./issue_spec.rb:29:in `block (2 levels) in <top (required)>'

Finished in 0.00161 seconds
1 example, 1 failure

Failed examples:

rspec ./issue_spec.rb:23 # Projects.for_user queries the correct shard