Add validation coverage for `CustomEmoji` shortcode value (#31906)

app/models/custom_emoji.rb

@@ -25,6 +25,7 @@ class CustomEmoji < ApplicationRecord
   include Attachmentable
 
   LIMIT = 256.kilobytes
+  MINIMUM_SHORTCODE_SIZE = 2
 
   SHORTCODE_RE_FRAGMENT = '[a-zA-Z0-9_]{2,}'
 
@@ -44,7 +45,7 @@ class CustomEmoji < ApplicationRecord
   normalizes :domain, with: ->(domain) { domain.downcase }
 
   validates_attachment :image, content_type: { content_type: IMAGE_MIME_TYPES }, presence: true, size: { less_than: LIMIT }
-  validates :shortcode, uniqueness: { scope: :domain }, format: { with: SHORTCODE_ONLY_RE }, length: { minimum: 2 }
+  validates :shortcode, uniqueness: { scope: :domain }, format: { with: SHORTCODE_ONLY_RE }, length: { minimum: MINIMUM_SHORTCODE_SIZE }
 
   scope :local, -> { where(domain: nil) }
   scope :remote, -> { where.not(domain: nil) }

spec/models/custom_emoji_spec.rb

@@ -84,4 +84,13 @@ RSpec.describe CustomEmoji, :attachment_processing do
       it { is_expected.to normalize(:domain).from(nil).to(nil) }
     end
   end
+
+  describe 'Validations' do
+    subject { Fabricate.build :custom_emoji }
+
+    it { is_expected.to validate_uniqueness_of(:shortcode).scoped_to(:domain) }
+    it { is_expected.to validate_length_of(:shortcode).is_at_least(described_class::MINIMUM_SHORTCODE_SIZE) }
+    it { is_expected.to allow_values('cats').for(:shortcode) }
+    it { is_expected.to_not allow_values('@#$@#$', 'X').for(:shortcode) }
+  end
 end