DEV: UserOption.user_tzinfo (#14088)

Provides a safe way to retrieve the timezone of a user.

This is not used in core yet, but used in multiple plugins.

spec/models/user_option_spec.rb

@@ -166,4 +166,28 @@ describe UserOption do
     end
 
   end
+
+  describe '.user_tzinfo' do
+    fab!(:user) { Fabricate(:user) }
+
+    context 'user with valid timezone given' do
+      before do
+        user.user_option.update(timezone: 'Europe/Paris')
+      end
+
+      it 'returns the expect timezone' do
+        expect(UserOption.user_tzinfo(user.id)).to eq(ActiveSupport::TimeZone.find_tzinfo('Europe/Paris'))
+      end
+    end
+
+    context 'user with invalid timezone given' do
+      before do
+        user.user_option.update(timezone: 'Catopia/Catcity')
+      end
+
+      it 'fallbacks to UTC' do
+        expect(UserOption.user_tzinfo(user.id)).to eq(ActiveSupport::TimeZone.find_tzinfo('UTC'))
+      end
+    end
+  end
 end