mock.js

mock.js

const getAppointments = Appointment => () => {
return Appointment.joins(:customer).where('customers.pays_a_lot = true').includes(:customer).order_by('customers.age DESC')
}

const dbmock = fakes => new Proxy({}, {
  get: (target, name) => {
    if(!fakes[name]) return this
    return fakes[name]
  }
)

test('gets appointments', () => {
 let fakeAppointments = [{ id: 1, title: 'blah' }]
 
 let appointments = getAppointments(dbmock({ order_by: () => fakeAppointments }))()

  expect(appointments[0].title).toEqual('blah')
})