Concatunate storages into new storage

Now we cat add new data to the old storage, which returns a new storage
containg first the new data and then the old data.
Plus a test for this, because it's not implemented now.

lib/rubella/storage.rb

@@ -25,6 +25,16 @@ module Rubella
       # TODO drop entries, if more than new length
     end
 
+    # Adds the data from the given storage to the own data and return this as a
+    # new Storage. Does not modify one of the storages. 
+    # 
+    # @param storage Rubella::Storage Storage with new data
+    # @return Rubella::Storage
+    #
+    def add storage
+      Storage.new (storage.data+@data), @length
+    end
+
   end
 
 end

spec/spec_helper.rb

@@ -0,0 +1,9 @@
+if ENV['SIMPLECOV']
+  require 'simplecov'
+  SimpleCov.start do
+    add_filter '_spec.rb'
+    add_filter 'spec_helper.rb'
+  end
+end
+
+require 'rubella'

spec/unit/rubella/storage/add_spec.rb

@@ -0,0 +1,13 @@
+require 'spec_helper'
+
+describe Rubella::Storage, '.add' do
+  
+  it "returns a new Storage with the given Storages data before the old" do
+    storage_1 = Rubella::Storage.new [3, 4, 5]
+    storage_2 = Rubella::Storage.new [0, 1, 2]
+
+    storage_new = storage_1.add storage_2
+    expect(storage_new.data).to eq([0, 1, 2, 3, 4, 5])
+  end
+
+end