Add model spec for `Tombstone` (#32697)

app/models/tombstone.rb

@@ -14,4 +14,6 @@
 
 class Tombstone < ApplicationRecord
   belongs_to :account
+
+  validates :uri, presence: true
 end

spec/fabricators/tombstone_fabricator.rb

@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+Fabricator(:tombstone) do
+  account
+  uri { sequence(:uri) { |i| "https://host.example/value/#{i}" } }
+end

spec/models/tombstone_spec.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe Tombstone do
+  describe 'Associations' do
+    it { is_expected.to belong_to(:account).required }
+  end
+
+  describe 'Validations' do
+    subject { Fabricate.build :tombstone }
+
+    it { is_expected.to validate_presence_of(:uri) }
+  end
+end