add test verifying deprecation notice is posted

Author: oreoshake

Gemfile

@@ -19,4 +19,5 @@ group :guard do
   gem "growl"
   gem "guard-rspec", platforms: [:ruby_19, :ruby_20, :ruby_21, :ruby_22, :ruby_23, :ruby_24]
   gem "rb-fsevent"
+  gem 'terminal-notifier-guard'
 end

spec/lib/secure_headers/configuration_spec.rb

@@ -12,6 +12,11 @@ module SecureHeaders
       expect(Configuration.get(Configuration::DEFAULT_CONFIG, internal: true)).to_not be_nil
     end
 
+    it "warns when using deprecated internal-ish #get API" do
+      expect(Kernel).to receive(:warn).once.with(/`#get` is deprecated/)
+      Configuration.get(Configuration::DEFAULT_CONFIG)
+    end
+
     it "has an 'noop' config" do
       expect(Configuration.get(Configuration::NOOP_CONFIGURATION, internal: true)).to_not be_nil
     end