Specs for Enumerable#one?

core/enumerable/one_spec.rb

@@ -1,5 +1,29 @@
 require File.expand_path('../../../spec_helper', __FILE__)
 
 describe "Enumerable#one?" do
-  it "needs to be reviewed for spec completeness"
+  ruby_version_is '1.8.7' do
+    describe "when block is given" do
+      it "returns true if block returns true once" do
+        ["ant", "bear", "cat"].one?{ |word| word.length == 4 }.should be_true
+      end
+
+      it "returns false if block evaluation are true more than once" do
+        ["ant", "bear"].one? { |word| word.length > 4 }.should be_false
+      end
+    end
+
+    describe "when block isn't given" do
+      it "returns true if only one element is true" do
+        [false, nil, true].one?.should be_true
+      end
+
+      it "returns false if two elements are true" do
+        [false, true, nil, true].one?.should be_false
+      end
+
+      it "returns false if two elements aren't false or nil" do
+        [false, true, nil, 99].one?.should be_false
+      end
+    end
+  end
 end