animal = ForeignKeySpec::Animal.create!(a: 'bear')
      zoo = ForeignKeySpec::Zoo.create!(z: 'bz')
      animal.zoos << zoo
      animal.save!

      # This write should not be necessary, but without it the test fails.
      zoo.animals << animal
      zoo.save!

      expect(zoo.animals).to eq([animal])
      zoo = ForeignKeySpec::Zoo.find(zoo.id)
      expect(zoo.animals).to eq([animal])