add failing spec and fix rails version check

lib/formtastic/util.rb

@@ -38,7 +38,11 @@ def rails4_1?
     end
 
     def deprecated_version_of_rails?
-      const_defined?(:Rails) && ::Rails::VERSION::MAJOR == 3 && ::Rails::VERSION::MINOR < 2 && ::Rails::VERSION::PATCH < 13
+      const_defined?(:Rails) && rails_version < Gem::Version.new("3.2.13")
+    end
+
+    def rails_version
+      Gem::Version.new(::Rails::VERSION::STRING)
     end
 
   end

spec/util_spec.rb

@@ -0,0 +1,59 @@
+# encoding: utf-8
+require 'spec_helper'
+
+describe 'Formtastic::Util' do
+
+  describe '.deprecated_version_of_rails?' do
+
+    subject { Formtastic::Util.deprecated_version_of_rails? }
+
+    context '3.0.0' do
+      before { allow(Formtastic::Util).to receive(:rails_version) { Gem::Version.new("3.0.0") } }
+      it 'should be true' do
+        expect(subject).to be_true
+      end
+    end
+
+    context '3.1.0' do
+      before { allow(Formtastic::Util).to receive(:rails_version) { Gem::Version.new("3.1.0") } }
+      it 'should be true' do
+        expect(subject).to be_true
+      end
+    end
+
+    context '3.2.12' do
+      before { allow(Formtastic::Util).to receive(:rails_version) { Gem::Version.new("3.2.12") } }
+      it 'should be true' do
+        expect(subject).to be_true
+      end
+    end
+
+    context '3.2.13' do
+      before { allow(Formtastic::Util).to receive(:rails_version) { Gem::Version.new("3.2.13") } }
+      it 'should be true' do
+        expect(subject).to be_false
+      end
+    end
+
+    context '3.2.14' do
+      before { allow(Formtastic::Util).to receive(:rails_version) { Gem::Version.new("3.2.14") } }
+      it 'should be true' do
+        expect(subject).to be_false
+      end
+    end
+
+    context '3.3.0' do
+      before { allow(Formtastic::Util).to receive(:rails_version) { Gem::Version.new("3.3.0") } }
+      it 'should be true' do
+        expect(subject).to be_false
+      end
+    end
+
+    context '4.0.0' do
+      before { allow(Formtastic::Util).to receive(:rails_version) { Gem::Version.new("4.0.0") } }
+      it 'should be true' do
+        expect(subject).to be_false
+      end
+    end
+  end
+end