* Rename NullAdapter to SimpleAdapter

* Introduce abstract Adapter class
* Organaze test structure to match convemtions

test/adapter/simple_adapter_test.rb

@@ -0,0 +1,24 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class Adapter
+      class SimpleAdapterTest < Minitest::Test
+        def setup
+          @profile = Profile.new({ name: 'Name 1', description: 'Description 1', comments: 'Comments 1' })
+          @profile_serializer = ProfileSerializer.new(@profile)
+
+          @adapter = SimpleAdapter.new(@profile_serializer)
+        end
+
+        def test_simple_adapter
+          assert_equal('{"name":"Name 1","description":"Description 1"}',
+                       @adapter.to_json)
+
+JSON
+        end
+      end
+    end
+  end
+end
+