Add specs configuration

spec/dummy/app/models/author.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+class Author < ApplicationRecord
+  has_many :posts
+  has_many :published_posts, -> { published }, class_name: 'Post'
+  has_many :recent_posts, -> { recents }, class_name: 'Post'
+
+  has_many :tags, through: :posts
+
+  has_one :profile, inverse_of: :author, dependent: :destroy
+
+  has_one_attached :avatar
+
+  accepts_nested_attributes_for :profile, allow_destroy: true
+
+  validates :email, format: { with: /\A[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}\z/i, message: 'Invalid email' }
+
+  validate -> {
+    errors.add( :base, 'Invalid age' ) if !age || age.to_i % 3 == 1
+  }
+
+  def to_s
+    "#{name} (#{age})"
+  end
+end