Implementation for single digit, test for 2 digits

lib/string_counter.rb

@@ -1,5 +1,5 @@
 class String
   def add
-    0 if empty?
+    to_i
   end
 end

spec/string_counter/string_counter_spec.rb

@@ -11,12 +11,18 @@
     context "a string with a single number" do
 
       it "returns the number" do
-        3.times do |i|
-          i.to_s.add.should == i
-        end
+        '1'.add.should == 1
       end
     end
 
+    context 'when dealing with more than 1 digit' do
+
+      it 'returns the sum of its parts' do
+        '1,2'.add.should == 3
+      end
+
+    end
+
   end
 end