Add ability to block words in usernames (#35407)

spec/models/username_block_spec.rb

@@ -0,0 +1,63 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe UsernameBlock do
+  describe '.matches?' do
+    context 'when there is an exact block' do
+      before do
+        Fabricate(:username_block, username: 'carriage', exact: true)
+      end
+
+      it 'returns true on exact match' do
+        expect(described_class.matches?('carriage')).to be true
+      end
+
+      it 'returns true on case insensitive match' do
+        expect(described_class.matches?('CaRRiagE')).to be true
+      end
+
+      it 'returns true on homoglyph match' do
+        expect(described_class.matches?('c4rr14g3')).to be true
+      end
+
+      it 'returns false on partial match' do
+        expect(described_class.matches?('foo_carriage')).to be false
+      end
+
+      it 'returns false on no match' do
+        expect(described_class.matches?('foo')).to be false
+      end
+    end
+
+    context 'when there is a partial block' do
+      before do
+        Fabricate(:username_block, username: 'carriage', exact: false)
+      end
+
+      it 'returns true on exact match' do
+        expect(described_class.matches?('carriage')).to be true
+      end
+
+      it 'returns true on case insensitive match' do
+        expect(described_class.matches?('CaRRiagE')).to be true
+      end
+
+      it 'returns true on homoglyph match' do
+        expect(described_class.matches?('c4rr14g3')).to be true
+      end
+
+      it 'returns true on suffix match' do
+        expect(described_class.matches?('foo_carriage')).to be true
+      end
+
+      it 'returns true on prefix match' do
+        expect(described_class.matches?('carriage_foo')).to be true
+      end
+
+      it 'returns false on no match' do
+        expect(described_class.matches?('foo')).to be false
+      end
+    end
+  end
+end