Challenge 1: A Model Spec — Solution

# spec/models/post_spec.rb
RSpec.describe Post, type: :model do
  it "is invalid without a title" do
    post = Post.new(title: nil)
    expect(post).to_not be_valid
  end

  it "belongs to a user" do
    expect(Post.reflect_on_association(:user).macro).to eq(:belongs_to)
  end
end

=begin
Notes:
- Post.new(title: nil) builds an in-memory record without saving it -- valid?
  runs the validations without touching the database, which is all this
  example needs.
- be_valid is RSpec's auto-generated matcher for the valid? predicate method
  every ActiveRecord model has; to_not be_valid calls post.valid? and expects
  false.
- reflect_on_association(:user) inspects Post's declared associations without
  needing an actual saved record -- .macro returns the association type
  (:belongs_to, :has_many, etc.) as a symbol, which is compared directly
  against what the model is expected to declare.
- Each example checks exactly one rule, matching the chapter's model-spec
  example (one for validates presence, one for belongs_to).
=end