Write tests with lazy variables

spec.js

describe('Invoice', function() {
  def('user', function() {
    return User.create({ role: 'member' });
  });
  
  def('invoice', function() {
    return $user.invoices.create({ price: 10, currency: 'USD' });
  });
  
  describe('by default', function() {
    it('has status "fraud" if amount does not equal to invoice amount', function() {
      $invoice.paid(1, 'USD');
      expect($invoice.status).to.equal('fraud');
    });
  });
  
  describe('when user is admin', function() {
    def('user', function() {
      return User.create({ role: 'admin' });
    });
    
    it('has status "paid" if amount does not equal to invoice amount', function() {
      $invoice.paid(1, 'USD');
      expect($invoice.status).to.equal('paid');
    });
  });
});