Added adjacency check between two vertices. Part of #9

lib/abstract_graph/graph.rb

@@ -25,3 +25,4 @@ class Graph
 require "abstract_graph/graph/delete_edge"
 require "abstract_graph/graph/change_vertex_name"
 require "abstract_graph/graph/change_edge_name"
+require "abstract_graph/graph/is_adjacent"

lib/abstract_graph/graph/is_adjacent.rb

@@ -0,0 +1,20 @@
+# required in "abstract_graph/graph"
+
+module AbstractGraph
+  class Graph
+
+    # returns whether or not v1 and v2 are joined by an edge
+    # p: String v1, v2 represents the names of the vertices
+    def is_adjacent?( v1, v2 )
+      vertices = [v1, v2].sort!
+
+      ( @edges.each_value.find do |e|
+        vertices == e.vertices.map do |v|
+          v.name
+        end.sort
+      end && true ) || false
+
+    end
+
+  end
+end

spec/abstract_graph/graph/is_adjacent_spec.rb

@@ -0,0 +1,38 @@
+require 'spec_helper'
+
+module AbstractGraph
+  module Composition
+    describe Graph do
+
+      before :all do
+        @vertex1 = "Vertex1"
+        @vertex2 = "Vertex2"
+        @vertex3 = "Vertex3"
+        @edge1 = "Edge1"
+        @edge2 = "Edge2"
+      end
+
+      before :each do
+        @graph = Graph.new
+        @graph.add_vertex @vertex1
+        @graph.add_vertex @vertex2
+        @graph.add_vertex @vertex3
+        @graph.add_edge @edge1, @vertex1, @vertex2
+        @graph.add_edge @edge2, @vertex2, @vertex3
+      end
+
+      describe "#is_adjacent?(String,String)" do
+
+        it "returns true if two vertices are joined with an edge" do
+          @graph.is_adjacent?( @vertex1, @vertex2 ).should be_true
+        end
+
+        it "returns false if two vertices are not joined with an edge" do
+          @graph.is_adjacent?( @vertex1, @vertex3 ).should be_false
+        end
+
+      end
+
+    end
+  end
+end