RSpec "double"

store.rb

class Store
  def foo
    Storage.store "abc", "bbc"
  end

#  def bar
#    storage = Storage.new
#    storage.some_instance_method "cnn"
#  end

  # I recommend that you instead set it up like this:
  def bar
    storage.some_instance_method "cnn"
  end

  # This way, you can stub #storage in specs, and it
  # becomes a modifyable integration point in the future. 
  def storage
    @storage ||= Storage.new
  end
end

# In spec

describe "#foo" do
  # You need a subject so that you can actually call the methods.
  # If you don't specify the subject, the subject just becomes
  # described_class.new
  # (In this case, Store.new)
  
  it "should call Storage.store" do
    # If you set #should_receive, you don't need to stub!
    # Storage.stub(:store)
    Storage.should_receive(:store).with("abc", "bbc")

    # Make sure you actually call the method. #should_receive isn't 
    # evaluated until after the example has run to completion. 
    subject.foo
  end
end

describe "#bar" do
  it "should call storage.some_instance_method" do
    # Doesn't matter what you name it. The name is just a helper 
    # that you can use for better feedback when the spec fails. 
    storage = double("storage")

# Is the above the right way to test "Storage" and "storage"?
#   Not exactly. What you're trying to specify is that "the storage
#   attribute can just be a double. What you really want is something more 
#   like this:
    subject.stub(:storage).and_return(storage)
    storage.should_receive(:some_instance_method).with("cnn")

    # Again, make sure to actually call the method
    subject.bar
  end
end