Challenge 2: A FactoryBot Factory — Solution

# spec/factories/posts.rb
FactoryBot.define do
  factory :post do
    title { "A perfectly reasonable title" }
    body  { "Some perfectly reasonable body text." }
    association :user
  end
end

# in a spec:
post = create(:post, title: "Overriding just the title")
post.title       # => "Overriding just the title"
post.body        # => "Some perfectly reasonable body text." (factory default, untouched)
post.user         # => an automatically-created User record

=begin
Notes:
- association :user tells FactoryBot to create a real User record (via a
  :user factory defined elsewhere) and assign it, rather than leaving
  user_id nil -- without this, saving the post would fail belongs_to's
  implicit presence validation (rails1-7).
- create(:post, title: "...") only overrides the title attribute passed in;
  every other attribute -- body, the user association -- falls back to
  whatever the factory defines by default.
- Using { } (a block) rather than a plain string for title and body means
  FactoryBot evaluates it fresh for every record created, avoiding all
  created posts sharing the exact same in-memory string object.
- create saves to the test database; build (not used here) would construct
  the same object without persisting it, useful for specs that don't need a
  saved record at all.
=end