Validate ValuatorGroup#name presence & uniqueness

Why:

ValuatorGroup name should be unique and present to be able to identify
correctly each of them.

How:
  - Adding a presence & uniqueness validation at the model
  - Adding a sequenced value for name attribute at its factory
  - Adding missing model spec that covers validations

app/models/valuator_group.rb

@@ -2,4 +2,6 @@ class ValuatorGroup < ActiveRecord::Base
   has_many :valuators
   has_many :valuator_group_assignments, dependent: :destroy, class_name: 'Budget::ValuatorGroupAssignment'
   has_many :investments, through: :valuator_group_assignments, class_name: 'Budget::Investment'
-end
+
+  validates :name, presence: true, uniqueness: true
+end

spec/factories.rb

@@ -62,6 +62,7 @@ FactoryBot.define do
   end
 
   factory :valuator_group, class: ValuatorGroup do
+    sequence(:name) { |n| "Valuator Group #{n}" }
   end
 
   factory :identity do

spec/models/valuator_group_spec.rb

@@ -0,0 +1,20 @@
+require 'rails_helper'
+
+describe ValuatorGroup do
+
+  describe 'Validations' do
+    it "should be valid" do
+      expect(build(:valuator_group)).to be_valid
+    end
+
+    it "should not be valid without a name" do
+      expect(build(:valuator_group, name: nil)).not_to be_valid
+    end
+
+    it "should not be valid with the same name as an existing one" do
+      create(:valuator_group, name: 'The Valuators')
+
+      expect(build(:valuator_group, name: 'The Valuators')).not_to be_valid
+    end
+  end
+end