Make graph dup do a deep copy. Closes #6

lib/abstract_graph/graph.rb

@@ -17,3 +17,4 @@ class Graph
 require "abstract_graph/graph/initialize"
 require "abstract_graph/graph/add_vertex"
 require "abstract_graph/graph/has_vertex"
+require "abstract_graph/graph/dup"

lib/abstract_graph/graph/dup.rb

@@ -0,0 +1,14 @@
+# required in "abstract_graph/graph"
+
+module AbstractGraph
+  class Graph
+
+    # does a deep copy of the graph
+    def dup
+      other = Graph.new
+      other.vertices = @vertices.dup
+      other
+    end
+
+  end
+end

spec/abstract_graph/graph/dup_spec.rb

@@ -0,0 +1,37 @@
+require 'spec_helper'
+
+module AbstractGraph
+  module Composition
+    describe Graph do
+
+      before :each do
+        @graph = Graph.new
+        @graph.add_vertex "MyVertex"
+      end
+
+      describe "#dup" do
+
+        it "returns a graph object" do
+          @graph.dup.should be_an_instance_of(Graph)
+        end
+
+        it "has a different id than the original graph" do
+          @graph.object_id.should_not == @graph.dup.object_id
+        end
+
+        it "copies over the existing vertices" do
+          graphdup = @graph.dup
+          graphdup.has_vertex?( "MyVertex" ).should be_true
+        end
+
+        it "will not modify the original if it is modified" do
+          graphdup = @graph.dup
+          graphdup.vertices.clear
+          @graph.vertices.size.should == 1
+        end
+
+      end
+
+    end
+  end
+end