thing.rb

class Thing < ActiveRecord::Base
  validates_presence_of :name
end

thing_spec.rb

require File.expand_path(File.dirname(__FILE__) + '/../spec_helper')

describe Thing do
  
  describe "with valid attributes" do
    it "has no errors" do
      thing = Thing.create!(:name => "slam!!!!!")
      thing.errors.on(:name).should be_nil
    end
  end
  
  describe "#save" do
    it "runs validations and stores errors" do
      thing = Thing.new
      thing.save
      thing.errors.on(:name).should == "can't be blank"
    end
  end
  
  describe "#save!" do
    it "runs validations and raises errors" do
      thing = Thing.new
      lambda do
        thing.save!
      end.should raise_error(ActiveRecord::RecordInvalid)
    end
  end

  describe "#create" do
    it "runs validations and stores errors" do
      thing = Thing.create
      thing.errors.on(:name).should == "can't be blank"
    end
  end
  
  describe "#create!" do
    it "runs validations and raises errors" do
      lambda do
        Thing.create!
      end.should raise_error(ActiveRecord::RecordInvalid)
    end
  end
end