it 'finds the existing person' do
  existing   = Person.create(username: 'Turnip', age: '49')
  found      = Person.create_with(attrs).find_or_create_by(query)

  expect(found.username).to eq('Turnip')
  expect(found.id).to eq(existing.id)
  expect(found.age).to eq(49)
end

  1) Mongoid::Criteria::Modifiable#create_with when called on the class when a method is chained when a write method is chained finds the existing person
     Failure/Error: expect(found.id).to eq(existing.id)

       expected: BSON::ObjectId('5ae8e6ba610db9d8a0266661')
            got: BSON::ObjectId('5ae8e6ba610db9d8a0266662')

       (compared using ==)

       Diff:
       @@ -1,2 +1,2 @@
       -BSON::ObjectId('5ae8e6ba610db9d8a0266661')
       +BSON::ObjectId('5ae8e6ba610db9d8a0266662')