Add some tests to enumerate how extensions should be stored in the schema output

activerecord/test/cases/adapters/postgresql/hstore_test.rb

@@ -35,6 +35,10 @@ def teardown
     @connection.execute 'drop table if exists hstores'
   end
 
+  def test_hstore_included_in_extensions
+    assert @connection.extensions.include?('hstore'), "extension list should include hstore"
+  end
+
   def test_hstore_enabled
     assert @connection.extension_enabled?('hstore')
   end

activerecord/test/cases/schema_dumper_test.rb

@@ -231,6 +231,17 @@ def test_schema_dump_includes_decimal_options
   end
 
   if current_adapter?(:PostgreSQLAdapter)
+    if ActiveRecord::Base.connection.supports_extensions?
+      def test_schema_dump_includes_extensions
+        connection = ActiveRecord::Base.connection
+        unless connection.extension_enabled?('hstore')
+          connection.enable_extension 'hstore'
+        end
+        output = standard_dump
+        assert_match %r{enable_extension "hstore"}, output
+      end
+    end
+
     def test_schema_dump_includes_xml_shorthand_definition
       output = standard_dump
       if %r{create_table "postgresql_xml_data_type"} =~ output