All good!

furlong.rb

@@ -1,7 +1,12 @@
 class Furlong
 
 	KM_PER_MILE = 1.60934
+	KM_PER_FURLONG = 0.201168
 	def miles_to_kilometers(miles)
 		miles * KM_PER_MILE
 	end
+
+	def furlongs_to_kilometers(furlongs)
+		furlongs * KM_PER_FURLONG
+	end
 end

furlong_spec.rb

@@ -12,4 +12,8 @@
 	it "converts a marathon: 26.219 miles to 42.194988 km" do
 		subject.miles_to_kilometers(26.219).should be_within(0.001).of(42.194988)
 	end
+
+	it "converts 1 furlong to 0.201168 kilometers" do
+		subject.furlongs_to_kilometers(1).should be_within(0.001).of(0.201168)
+	end
 end

furlong_test.rb

@@ -15,6 +15,11 @@ def test_marathon
 		assert_in_delta 42.194, km, 0.01
 	end
 
+	def test_furlong
+		km = Furlong.new.furlongs_to_kilometers(1)
+		assert_in_delta 0.201168, km, 0.001
+	end
+
 end
 
 describe Furlong do