Add an model_subclass generator.

This generator creates a new model as a subclass of an existing model and the unit test for that model.  Lets users avoid having to manually delete the fixtures and migration or remember to pass those arguments.

[#2702 state:committed]

Signed-off-by: Michael Koziarski <michael@koziarski.com>

railties/lib/rails_generator/generators/components/model_subclass/USAGE

@@ -0,0 +1,13 @@
+Description:
+    Create a model subclass of parent, used for Single Table Inheritance.
+
+    Both subclass and parent name can be either CamelCased or under_scored.
+
+    This generates a model class in app/models and a unit test in test/unit.
+
+Examples:
+    `./script/generate model_subclass admin user`
+
+        creates an Admin model, which will inheritate from User model, test:
+            Model:      app/models/admin.rb
+            Test:       test/unit/admin_test.rb

railties/lib/rails_generator/generators/components/model_subclass/model_subclass_generator.rb

@@ -0,0 +1,32 @@
+class ModelSubclassGenerator < Rails::Generator::NamedBase
+  default_options :skip_unit_test => false
+
+  def manifest
+    record do |m|
+      # Check for class naming collisions.
+      m.class_collisions class_name, "#{class_name}Test"
+
+      # Model and test directories.
+      m.directory File.join('app/models', class_path)
+      m.directory File.join('test/unit', class_path)
+
+      # Model class and unit test
+      m.template 'model.rb',      File.join('app/models', class_path, "#{file_name}.rb"),     :assigns => assigns
+      m.template 'unit_test.rb',  File.join('test/unit', class_path, "#{file_name}_test.rb"), :assigns => assigns
+
+    end
+  end
+
+  protected
+    def banner
+      "Usage: #{$0} #{spec.name} Subclass Parent"
+    end
+
+    def assigns
+      {:parent_class_name => parent_class_name}
+    end
+
+    def parent_class_name
+      @args.first.try(:camelize) || usage
+    end
+end

railties/lib/rails_generator/generators/components/model_subclass/templates/model.rb

@@ -0,0 +1,3 @@
+class <%= class_name %> < <%= parent_class_name %>
+
+end

railties/lib/rails_generator/generators/components/model_subclass/templates/unit_test.rb

@@ -0,0 +1,8 @@
+require 'test_helper'
+
+class <%= class_name %>Test < ActiveSupport::TestCase
+  # Replace this with your real tests.
+  test "the truth" do
+    assert true
+  end
+end

railties/test/generators/rails_model_subclass_generator_test.rb

@@ -0,0 +1,15 @@
+require 'generators/generator_test_helper'
+
+class RailsModelSubclassGeneratorTest < GeneratorTestCase
+
+  def test_model_subclass_generates_resources
+    run_generator('model_subclass', %w(Car Product))
+
+    assert_generated_model_for :car, "Product"
+    assert_generated_unit_test_for :car
+  end
+
+  def test_model_subclass_must_have_a_parent_class_name
+    assert_raise(Rails::Generator::UsageError) { run_generator('model_subclass', %w(Car)) }
+  end
+end