Add FactoryGirl.lint to ensure all factories are valid

This commit adds FactoryGirl.lint, which iterates over each defined
factory, builds it, and ensures it is valid. If any factories are
invalid, an exception is raised and includes the names of each invalid
factory.

lib/factory_girl.rb

@@ -54,6 +54,26 @@ module FactoryGirl
     @configuration = nil
   end
 
+  def self.lint
+    invalid_factories = FactoryGirl.factories.select do |factory|
+      built_factory = FactoryGirl.build(factory.name)
+
+      if built_factory.respond_to?(:valid?)
+        !built_factory.valid?
+      end
+    end
+
+    if invalid_factories.any?
+      error_message = <<-ERROR_MESSAGE.strip
+The following factories are invalid:
+
+#{invalid_factories.map {|factory| "* #{factory.name}" }.join("\n")}
+      ERROR_MESSAGE
+
+      raise InvalidFactoryError, error_message
+    end
+  end
+
   class << self
     delegate :factories, :sequences, :traits, :callbacks, :strategies, :callback_names,
       :to_create, :skip_create, :initialize_with, :constructor, :duplicate_attribute_assignment_from_initialize_with,

lib/factory_girl/errors.rb

@@ -19,4 +19,7 @@ module FactoryGirl
 
   # Raised when a method is defined in a factory or trait with arguments
   class MethodDefinitionError < RuntimeError; end
+
+  # Raised when any factory is considered invalid
+  class InvalidFactoryError < RuntimeError; end
 end

spec/acceptance/lint_spec.rb

@@ -0,0 +1,55 @@
+require 'spec_helper'
+
+describe 'FactoryGirl.lint' do
+  it 'raises when a factory is invalid' do
+    define_model 'User', name: :string do
+      validates :name, presence: true
+    end
+
+    define_model 'AlwaysValid'
+
+    FactoryGirl.define do
+      factory :user do
+        factory :admin_user
+      end
+
+      factory :always_valid
+    end
+
+    error_message = <<-ERROR_MESSAGE.strip
+The following factories are invalid:
+
+* user
+* admin_user
+    ERROR_MESSAGE
+
+    expect do
+      FactoryGirl.lint
+    end.to raise_error FactoryGirl::InvalidFactoryError, error_message
+  end
+
+  it 'does not raise when all factories are valid' do
+    define_model 'User', name: :string do
+      validates :name, presence: true
+    end
+
+    FactoryGirl.define do
+      factory :user do
+        name 'assigned'
+      end
+    end
+
+    expect { FactoryGirl.lint }.not_to raise_error
+  end
+
+  it 'supports models which do not respond to #valid?' do
+    define_class 'Thing'
+
+    FactoryGirl.define do
+      factory :thing
+    end
+
+    expect(Thing.new).not_to respond_to(:valid?)
+    expect { FactoryGirl.lint }.not_to raise_error
+  end
+end