Add specs for Data subclass and empty Data definition

Author: headius

core/data/fixtures/classes.rb

@@ -9,5 +9,13 @@ def self.name
     end
 
     class DataSubclass < Data; end
+
+    MeasureSubclass = Class.new(Measure) do
+      def initialize(amount:, unit:)
+        super
+      end
+    end
+
+    Empty = Data.define()
   end
 end

core/data/initialize_spec.rb

@@ -60,4 +60,15 @@
       e.message.should.include?("unknown keyword: :system")
     }
   end
+
+  it "supports super from a subclass" do
+    ms = DataSpecs::MeasureSubclass.new(amount: 1, unit: "km")
+
+    ms.amount.should == 1
+    ms.unit.should == "km"
+  end
+
+  it "supports Data with no fields" do
+    -> { DataSpecs::Empty.new }.should_not raise_error
+  end
 end