RSpec matcher to test nested attributes

gistfile1.rb

RSpec::Matchers.define :accept_nested_attributes_for do |association|
  @association = association

  match_for_should do |record|
    @record = record
    matches_against?(true)
  end

  match_for_should_not do |record|
    @record = record
    matches_against?(false)
  end

  def matches_against?(compare)
    raise "The accept_nested_attributes_for matcher requires an association; use subject.should accept_nested_attributes_for(:association)" unless @association
    
    @record.class.instance_methods.include?("#{@association}_attributes=".to_sym) == compare
  end

  failure_message_for_should do |actual|
    "expect to accept nested attributes for #{@association.inspect}"
  end

  failure_message_for_should_not do |actual|
    "expect to reject nested_attributes for #{@association.inspect}"
  end

  description do
    "accept nested attributes for #{@association.inspect}"
  end
end