You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: sales_by_category_test.rb
    path of file: ./repos/workarea/core/test/queries/workarea/reports
    
    the code of the file until where you have to start completion: require 'test_helper'

module Workarea
  module Reports
    class SalesByCategoryTest < TestCase
      setup :add_data, :time_travel

      def add_data
        Metrics::CategoryByDay.inc(
          key: { category_id: 'foo' },
          at: Time.zone.local(2018, 10, 27),
          orders: 1,
          units_sold: 2,
          merchandise: 10.to_m,
          discounts: 0.to_m,
          tax: 0.7.to_m,
          revenue: 10.to_m
        )

        Metrics::CategoryByDay.inc(
          key: { category_id: 'foo' },
          at: Tim
    
      def test_grouping_and_summing
        report = SalesByCategory.new
        assert_equal(2, report.results.length)

        foo = report.results.detect { |r| r['_id'] == 'foo' }
        assert_equal(6, foo['orders'])
        assert_equal(12, foo['units_sold'])
        assert_equal(60, foo['merchandise'])
        assert_equal(-8, foo['discounts'])
        assert_equal(4.2, foo['tax'])
        assert_equal(52, foo['revenue'])

        bar = report.results.detect { |r| r['_id'] == 'bar' }
        assert_equal(9, bar['orders'])
        assert_equal(15, bar['units_sold'])
        assert_equal(63, bar['merchandise'])
        assert_equal(-10, bar['discounts'])
        assert_equal(4.2, foo['tax'])
        assert_equal(53, bar['revenue'])
      end