Add missing image model spec. Add shared specs to check image validations at any imageable model

app/models/direct_upload.rb

@@ -0,0 +1,28 @@
+class DirectUpload
+  include ActiveModel::Validations
+
+  attr_accessor :resource, :resource_type, :resource_id, :resource_relation,
+                :attachment, :cached_attachment
+
+  validates_presence_of :attachment, :resource_type, :resource_relation
+  validate :parent_resource_attachment_validations,
+           if: -> { attachment.present? && resource_type.present? && resource_relation.present? }
+
+  def parent_resource_attachment_validations
+    # Proposal or Budget::Investment
+    resource = resource_type.constantize.find_or_initialize_by(id: resource_id)
+
+    # Document or Image
+    relation = if resource.class.reflections[resource_relation].macro == :has_one
+                 resource.send("build_#{resource_relation}", attachment: attachment)
+               else
+                 resource.send(resource_relation).build(attachment: attachment)
+               end
+    relation.valid?
+
+    if relation.errors.has_key? :attachment
+      errors[:attachment] = relation.errors[:attachment]
+    end
+  end
+
+end