boolean_validator.rb

class BooleanValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    unless is_a_boolean? value
      record.errors[attribute] << (options[:message] || "is not valid") 
    end
  end

  def is_a_boolean? value
    !!value == value
  end
end

boolean_validator_spec.rb

require 'active_model'
require_relative '../../app/validators/boolean_validator'

class Person
  attr_accessor :foobar
  include ActiveModel::Validations

  validates :foobar, :boolean => true
end

describe BooleanValidator do
  subject { Person.new }

  it "is valid if attribute is true" do
    subject.foobar = true
    expect(subject.valid?).to eq true
  end

  it "is valid if attribute is false" do
    subject.foobar = false
    expect(subject.valid?).to eq true
  end

  it "is not valid if attribute is a string" do
    subject.foobar = "hello"
    expect(subject.valid?).to eq false
  end

  it "is not valid if attribute is a string having a number" do
    subject.foobar = "1"
    expect(subject.valid?).to eq false

    subject.foobar = "a1"
    expect(subject.valid?).to eq false
  end

  it "is not valid if attribute is an integer" do
    subject.foobar = 1
    expect(subject.valid?).to eq false
  end

end

factory_spec.rb

# https://github.com/thoughtbot/factory_girl/wiki/Testing-all-Factories-(with-RSpec)

require 'spec_helper'

describe 'validate FactoryGirl factories' do
  FactoryGirl.factories.each do |factory|
    context "with factory for :#{factory.name}" do
      subject { FactoryGirl.build(factory.name) }
      
      it "is valid" do
        subject.should be_valid, subject.errors.full_messages
      end
    end
  end
end

loan.rb

require_dependency 'boolean_validator'

class Loan < ActiveRecord::Base
  validates :borrower_male, boolean: true, presence: true
end

loans_factory.rb

FactoryGirl.define do
  factory :loan do
    borrower_male     false
  end
end

factory_spec.rb fails even though boolean_validator_spec.rb is a success. why ?

$ rspec spec/models/factory_spec.rb

validate FactoryGirl factories with factory for :loan is valid
     Failure/Error: subject.should be_valid, subject.errors.full_messages
     []

fixed. check the webapp project