Some rspec macros to verify Rails model validations

examples.rb

# Require fields.
it_should_require :wish, :author, :title, :body, :signature

# Validate string lengths
it_should_validate_strings :body => 1024, :title => 255, :signature => 25

# Strings can be absent. Default length is 255, like Rails.
it_should_validate_strings :story => 10000,
                           :blurb => {:optional => true},
                           :tagline => {:optional => true}

# Optional with a non-default length.
it_should_validate_strings :note => {:length => 1024, :optional => true}

# Specify a specific Fixjour builder.
use_builder :video_attachment # => new_video_attachment

spec_validation_macros.rb

module Spec::Example::ExampleGroupMethods
  def use_builder(builder) # Using Fixjour
    module_eval <<-BUILDER
      def object_builder
        #{builder.inspect}
      end
    BUILDER
  end

  def it_should_require(*fields)
    @required_fields = fields
    instance_eval <<-REQUIREMENTS
      it_should_behave_like "things with required fields"
    REQUIREMENTS
  end

  def it_should_validate_strings(string_lengths)
    @string_lengths_to_validate = string_lengths
    instance_eval <<-REQUIREMENTS
      it_should_behave_like "things with strings"
    REQUIREMENTS
  end
end

shared_examples_for "object builders" do
  def new_object(*args)
    builder_name = described_class.name.underscore
    builder_name = object_builder if respond_to?(:object_builder)
    send("new_#{builder_name}", *args)
  end
end

shared_examples_for "things with required fields" do
  it_should_behave_like "object builders"

  @required_fields.each do |field|
    it "must have a(n) #{field}" do
      new_object(field => nil).should_not be_valid
    end
  end
end

shared_examples_for "things with strings" do
  it_should_behave_like "object builders"

  @string_lengths_to_validate.each do |field, options|
    if options.is_a?(Fixnum)
      max_length = options
    else
      max_length = options.fetch(:length, 255)
      allow_blank = options.fetch(:optional, false)
    end

    unless allow_blank
      it "can't have an empty #{field}" do
        new_object(field => '').should_not be_valid
      end
    end

    it "can't have a loooooong #{field}" do
      new_object(field => 'a'*(max_length+1)).should_not be_valid
    end

    [1, rand(max_length)+1, max_length].each do |length|
      it "can have a reasonably sized #{field}" do
        new_object(field => 'a'*length).should be_valid
      end
    end
  end
end