Adds a fake method with no test coverage to test Undercover gem

lib/spree/core/fake_method.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+module Spree
+  module Core
+    class FakeMethod
+      # testing Undercover!
+      # it's a random method, with no test coverage
+      def square(number)
+        number * number
+      end
+    end
+  end
+end