Add test for UserDecorator#avatar_url

spec/decorators/user_decorator_spec.rb

@@ -0,0 +1,27 @@
+require 'spec_helper'
+
+describe UserDecorator do
+
+  let(:decorator) { described_class.new(user) }
+  let(:user) { double('user', avatar_url: avatar_url, email: 'foo@email.com') }
+
+  describe '#avatar_url' do
+    subject { decorator.avatar_url }
+
+    context "when avatar_url present on user" do
+      let(:avatar_url) { 'http://avatar/url' }
+
+      it { should eq('http://avatar/url') }
+    end
+
+    context "when avatar_url missing on user" do
+      let(:avatar_url) { nil }
+
+      it {
+        should
+          eq('//gravatar.com/avatar/9dcfeb70fe212ea12562dddd22b0fc92?s=128')
+      }
+    end
+  end
+
+end