Rails unit testing - Find out why exactly the assertion failed

Question

I have written a unit test whose assertion fails - I would like to find out why, without having to inspect every attribute of the model.

Here is my test:

test "a correct document should be saved" do
  document = documents(:one)
  document.pdf = File.new("test/files/document_test_file.pdf")
  assert document.save
end

And here is the fixture:

one:
  user_id: 1
  title: MyString
  published_on: 2012-12-06
  tags: MyText
  language: MyString

Apparently, something is missing and the document cannot be saved. But how do I find out what exactly is missing? Is there any advanced assertion method to do this?

And my model:

class Document < ActiveRecord::Base
  attr_accessible :language, :pdf, :pdf_file_name, :published_on, :tags, :title, :user_id

  # Validations
  validates_presence_of :language, :published_on, :tags, :title, :user
  validates_date :published_on, on_or_before: Date.current,
                                on_or_before_message: "must be today or earlier"
  validates :user_id, numericality: { only_integer: true, greater_than: 0 }
  validates :pdf, attachment_presence: true

  # Relations
  belongs_to :user

  # Paperclip
  has_attached_file :pdf
end

Answer 1

An easy way to find out why save fails is to call save! instead. The exception will give you enough information.

Another way is to call valid? and then puts errors.

Answer 2

How about:

assert document.save, document.errors.full_messages.join(" ")