respond_with について調べてみた ref: http://qiita.com/blueplanet/items/9587b31f1805d80fd4c3

file0.txt

it "re-renders the 'new' template" do
  # Trigger the behavior that occurs when invalid params are submitted
  Journal.any_instance.stub(:save).and_return(false)
  post :create, {:journal => { "title" => "invalid title" }}, valid_session
  response.should render_template(:new)
end

it "re-renders the 'edit' template" do
  journal = Journal.create! valid_attributes
  # Trigger the behavior that occurs when invalid params are submitted
  Journal.any_instance.stub(:save).and_return(false)
  put :update, {:id => journal.to_param, :journal => { "title" => "invalid title" }}, valid_session
  response.should render_template(:edit)
end

it "updates the requested journal" do
  journal = Journal.create! valid_attributes
  # Assuming there are no other journals in the database, this
  # specifies that the Journal created on the previous line
  # receives the :update_attributes message with whatever params are
  # submitted in the request.
  Journal.any_instance.should_receive(:update).with({ "title" => "MyString" })
  put :update, {:id => journal.to_param, :journal => { "title" => "MyString" }}, valid_session
end

file1.txt

Failures:

  1) JournalsController PUT update with invalid params re-renders the 'edit' template
     Failure/Error: response.should render_template(:edit)
       expecting <"edit"> but rendering with <[]>
     # ./spec/controllers/journals_controller_spec.rb:122:in `block (4 levels) in <top (required)>'
     # -e:1:in `<main>'

  2) JournalsController POST create with invalid params re-renders the 'new' template
     Failure/Error: response.should render_template(:new)
       expecting <"new"> but rendering with <[]>
     # ./spec/controllers/journals_controller_spec.rb:78:in `block (4 levels) in <top (required)>'
     # -e:1:in `<main>'

  3) JournalsController PUT update with valid params updates the requested journal
     Failure/Error: Unable to find matching line from backtrace
       Exactly one instance should have received the following message(s) but didn't: update

file3.txt

it "re-renders the 'new' template" do
  # Trigger the behavior that occurs when invalid params are submitted
  # Journal.any_instance.stub(:save).and_return(false)
  post :create, {:journal => { "title" => nil }}, valid_session
  response.should render_template(:new)
end

it "re-renders the 'edit' template" do
  journal = Journal.create! valid_attributes
  # Trigger the behavior that occurs when invalid params are submitted
  # Journal.any_instance.stub(:save).and_return(false)
  put :update, {:id => journal.to_param, :journal => { "title" => nil }}, valid_session
  response.should render_template(:edit)
end

it "updates the requested journal" do
  journal = Journal.create! valid_attributes
  # Assuming there are no other journals in the database, this
  # specifies that the Journal created on the previous line
  # receives the :update_attributes message with whatever params are
  # submitted in the request.
  Journal.any_instance.should_receive(:update_attributes).with({ "title" => "MyString" })
  put :update, {:id => journal.to_param, :journal => { "title" => "MyString" }}, valid_session
end

responder.rb#L192

def navigation_behavior(error)
  if get?
    raise error
  elsif has_errors? && default_action
    render :action => default_action
  else
    redirect_to navigation_location
  end
end
...
def has_errors?
  resource.respond_to?(:errors) && !resource.errors.empty?
end