Generates Task model and adds relative unit tests

app/models/activity.rb

@@ -4,6 +4,8 @@ class Activity < ApplicationRecord
   has_one :joined_user_activity
   has_one :user, :through => :joined_user_activity
 
+  has_many :tasks
+
   validates :name, presence: true
   validates :author, presence: true
 end

app/models/task.rb

@@ -0,0 +1,7 @@
+class Task < ApplicationRecord
+  validates :name, presence: true
+  validates :user, presence: true
+
+  belongs_to :activity
+  belongs_to :user
+end

app/models/user.rb

@@ -9,5 +9,7 @@ class User < ApplicationRecord
   has_many :joined_user_activities
   has_many :activities, :through => :joined_user_activities
 
+  has_many :tasks
+
   has_secure_password
 end