Added a 'generates_subclass' class method

Allows abstract parent classes to specify which concrete subclass
should be generated by default.

lib/object_daddy.rb

@@ -26,6 +26,11 @@ module ClassMethods
     # Creates a valid instance of this class, using any known generators. The
     # generated instance is yielded to a block if provided.
     def spawn(args = {})
+      if @concrete_subclass_name
+        return block_given? \
+          ? const_get(@concrete_subclass_name).spawn(args) {|instance| yield instance} \
+          : const_get(@concrete_subclass_name).spawn(args)
+      end
       gather_exemplars
       generate_values(args)
       instance = new(args)
@@ -78,6 +83,10 @@ def generator_for(handle, args = {}, &block)
         raise ArgumentError, "a block, :class generator, :method generator, or value must be specified to generator_for"
       end
     end
+
+    def generates_subclass(subclass_name)
+      @concrete_subclass_name = subclass_name.to_s
+    end
 
     def gather_exemplars
       return if exemplars_generated

spec/object_daddy_spec.rb

@@ -438,6 +438,25 @@ def self.generator_value_method(prev)
     @class.generator_for :foo => 5
     @class.spawn(:foo => false).foo.should be(false)
   end
+
+  describe 'for an abstract parent class' do
+    before :each do
+      Widget = Class.new(OpenStruct) { include ObjectDaddy }
+      SubWidget = Class.new(Widget) {include ObjectDaddy }
+      Widget.stubs(:exemplar_path).returns(@file_path)
+      SubWidget.stubs(:exemplar_path).returns(File.join(@file_path, 'sub_widget_exemplar.rb'))
+    end
+
+    it 'should generate an instance of a specified concrete subclass (specced using a symbol)' do
+      Widget.generates_subclass :SubWidget
+      Widget.spawn.should be_instance_of SubWidget
+    end
+
+    it 'should generate an instance of a specified concrete subclass (specced using a string)' do
+      Widget.generates_subclass 'SubWidget'
+      Widget.spawn.should be_instance_of SubWidget
+    end
+  end
 
   describe 'for a subclass' do
     before :each do
@@ -478,7 +497,7 @@ def self.generator_value_method(prev)
         SubWidget.spawn.blah.should == 'blip'
       end
     end
-    
+
     describe 'using generators called directly' do
       it 'should use generators from the parent class' do
         @class.generator_for :blah do |prev| 'blah'; end