Should I use my own application's abstractions for test setup?

When doing test setup, is it better to use low-level APIs to get my system in the right state, or use the same abstractions that my application would use? I'm specifically interested in what promotes long-term maintainability in large codebases.

Example (in Ruby, but my question is language-agnostic):

A User can buy an Item using the Sale class:

class User
  attr_accessor :join_source, :status

  def web_join!
    @join_source = 'web'
    @status = 'rookie'
  end

  def promote!
    @status = 'veteran'
  end

  def web_rookie?
    join_source == 'web' && status == 'rookie'
  end
end

class Sale
  attr_reader :item, :user

  def initialize(item, user)
    @item = item
    @user = user
  end

  def finalize
    item.owner == user
    if user.web_rookie?
      Email.send_web_rookie_receipt(user)
    end
  end
end

In testing Sale, I will need to create a user in various states. I can either user low-level APIs:

user = User.new
user.join_source = 'web'
user.status = 'rookie'
# test that the send_web_rookie_receipt goes out
user.status = 'veteran'
# test that the send_web_rookie_receipt does not goes out

Or the API that User exposes:

user = User.new
user.web_join!
# test that the send_web_rookie_receipt goes out
user.promote!
# test that the send_web_rookie_receipt does not goes out