Pending example models minimal coverage (#23912)

spec/models/marker_spec.rb

@@ -2,6 +2,15 @@
 
 require 'rails_helper'
 
-RSpec.describe Marker, type: :model do
-  pending "add some examples to (or delete) #{__FILE__}"
+describe Marker do
+  describe 'validations' do
+    describe 'timeline' do
+      it 'must be included in valid list' do
+        record = described_class.new(timeline: 'not real timeline')
+
+        expect(record).to_not be_valid
+        expect(record).to model_have_error_on_field(:timeline)
+      end
+    end
+  end
 end