Add specs for Timelog model.

app/models/timelog.rb

 class Timelog < ActiveRecord::Base
+  validates :time_spent, :trackable, presence: true
+
   belongs_to :trackable, polymorphic: true
 end

spec/factories/timelogs.rb

+# Read about factories at https://github.com/thoughtbot/factory_girl
+
+FactoryGirl.define do
+  factory :timelog do
+    time_spent 3600
+    association :trackable, factory: :issue
+  end
+end

spec/models/timelog_spec.rb

+require 'rails_helper'
+
+RSpec.describe Timelog, type: :model do
+  subject { build(:timelog) }
+
+  it { is_expected.to be_valid }
+
+  it { is_expected.to validate_presence_of(:time_spent) }
+  it { is_expected.to validate_presence_of(:trackable) }
+end