Add park <-> alert relations

spec/models/alert_spec.rb

@@ -1,5 +1,9 @@
 require 'rails_helper'
 
 RSpec.describe Alert, type: :model do
-  pending "add some examples to (or delete) #{__FILE__}"
+  describe "#park" do
+    it "has a park" do
+      expect(alerts(:one).park).to eq(parks(:one))
+    end
+  end
 end