Add class name to enum validation exception message

Unify enum without column exception message

Update enum_test for new exception message

activerecord/lib/active_record/enum.rb

@@ -249,7 +249,7 @@ def _enum(name, values, prefix: nil, suffix: nil, scopes: true, instance_methods
 
         decorate_attributes([name]) do |_name, subtype|
           if subtype == ActiveModel::Type.default_value
-            raise "Undeclared attribute type for enum '#{name}'. Enums must be" \
+            raise "Undeclared attribute type for enum '#{name}' in #{self.name}. Enums must be" \
               " backed by a database column or declared with an explicit type" \
               " via `attribute`."
           end

activerecord/test/cases/enum_test.rb

@@ -1057,13 +1057,14 @@ def self.name
 
   test "raises for attributes with undeclared type" do
     klass = Class.new(Book) do
+      def self.name; "Book"; end
       enum typeless_genre: [:adventure, :comic]
     end
 
     error = assert_raises(RuntimeError) do
       klass.type_for_attribute(:typeless_genre)
     end
-    assert_match "Undeclared attribute type for enum 'typeless_genre'", error.message
+    assert_match "Undeclared attribute type for enum 'typeless_genre' in Book", error.message
   end
 
   test "supports attributes declared with a explicit type" do