Added a performance test in order to compare speed and memory usage o…

…f the two different approaches (+ vs add)

spec/performance_spec.rb

@@ -0,0 +1,30 @@
+require 'memory_profiler'
+
+RSpec.describe "Performance" do
+
+  it "sum 'in place'" do
+    t = Time.now
+    report = MemoryProfiler.report do
+      ya = Yarray.new(2018)
+      1.upto(1000).each do |n|
+        ya.add(Yarray.new(2018, value: n))
+      end
+      puts ya.to_s
+    end
+    puts Time.now-t
+    report.pretty_print
+  end
+
+  it "result of sum in a new yarray" do
+    t = Time.now
+    report = MemoryProfiler.report do
+      ya = Yarray.new(2018)
+      1.upto(1000).each do |n|
+        ya += Yarray.new(2018, value: n)
+      end
+      puts ya.to_s
+    end
+    puts Time.now-t
+    report.pretty_print
+  end
+end