Add comment model and its tests

app/models/comment.rb

@@ -0,0 +1,8 @@
+class Comment < ApplicationRecord
+  belongs_to :user
+  belongs_to :post
+  belongs_to :parent, class_name: 'Comment', optional: true
+  has_many :children, class_name: 'Comment', foreign_key: 'parent_id', dependent: :destroy
+
+  validates :body, presence: true, length: { minimum: 4 }
+end

db/migrate/20190916131938_create_comments.rb

@@ -0,0 +1,12 @@
+class CreateComments < ActiveRecord::Migration[6.0]
+  def change
+    create_table :comments do |t|
+      t.text :body
+      t.references :user, null: false, foreign_key: true
+      t.references :post, null: false, foreign_key: true
+      t.references :parent, foreign_key: { to_table: :comments }
+
+      t.timestamps
+    end
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2019_08_26_154118) do
+ActiveRecord::Schema.define(version: 2019_09_16_131938) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -23,6 +23,18 @@ ActiveRecord::Schema.define(version: 2019_08_26_154118) do
     t.index ["name"], name: "index_boards_on_name", unique: true
   end
 
+  create_table "comments", force: :cascade do |t|
+    t.text "body"
+    t.bigint "user_id", null: false
+    t.bigint "post_id", null: false
+    t.bigint "parent_id"
+    t.datetime "created_at", precision: 6, null: false
+    t.datetime "updated_at", precision: 6, null: false
+    t.index ["parent_id"], name: "index_comments_on_parent_id"
+    t.index ["post_id"], name: "index_comments_on_post_id"
+    t.index ["user_id"], name: "index_comments_on_user_id"
+  end
+
   create_table "post_statuses", force: :cascade do |t|
     t.string "name", null: false
     t.string "color", null: false
@@ -65,6 +77,9 @@ ActiveRecord::Schema.define(version: 2019_08_26_154118) do
     t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
   end
 
+  add_foreign_key "comments", "comments", column: "parent_id"
+  add_foreign_key "comments", "posts"
+  add_foreign_key "comments", "users"
   add_foreign_key "posts", "boards"
   add_foreign_key "posts", "post_statuses"
   add_foreign_key "posts", "users"

spec/factories/comments.rb

@@ -0,0 +1,8 @@
+FactoryBot.define do
+  factory :comment do
+    body { "MyText" }
+    user
+    post
+    parent { nil }
+  end
+end

spec/models/comment_spec.rb

@@ -0,0 +1,50 @@
+require 'rails_helper'
+
+RSpec.describe Comment, type: :model do
+  let(:comment) { FactoryBot.build(:comment) }
+
+  it 'should be valid' do
+    expect(comment).to be_valid
+  end
+
+  it 'has a body' do
+    nil_body = FactoryBot.build(:comment, body: nil)
+    empty_body = FactoryBot.build(:comment, body: '')
+
+    expect(nil_body).to be_invalid
+    expect(empty_body).to be_invalid
+  end
+
+  it 'has a body with 4 or more characters' do
+    short_body = FactoryBot.build(:comment, body: 'a' * 3)
+
+    expect(short_body).to be_invalid
+  end
+
+  it 'can have no parent' do
+    no_parent = FactoryBot.build(:comment, parent: nil)
+
+    expect(no_parent).to be_valid
+    expect(no_parent.parent).to be_nil
+  end
+
+  it 'can have a parent' do
+    parent = FactoryBot.build(:comment)
+    child = FactoryBot.build(:comment, parent: parent)
+
+    expect(child).to be_valid
+    expect(child.parent).to eq(parent)
+  end
+
+  it 'can have no children' do
+    expect(comment.children).to be_empty
+  end
+
+  it 'can have 1+ children' do
+    parent = FactoryBot.create(:comment)
+    child1 = FactoryBot.create(:comment, parent: parent)
+    child2 = FactoryBot.create(:comment, parent: parent)
+
+    expect(parent.children.length).to eq(2)
+  end
+end