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: group_by_time_test.rb
    path of file: ./repos/workarea/admin/test/view_models/workarea/admin/reports
    
    the code of the file until where you have to start completion: require 'test_helper'

module Workarea
  module Admin
    module Reports
      class GroupByTimeTest < TestCase
        def test_get_period_for
          view_model = SalesOverTimeViewModel.new
          assert_equal('2017', view_model.get_period_f
    
        def test_get_period_for
          view_model = SalesOverTimeViewModel.new
          assert_equal('2017', view_model.get_period_for('year' => 2017))
          assert_equal('2018-11', view_model.get_period_for('year' => 2018, 'month' => 11))
          assert_equal('2018-10-29', view_model.get_period_for('year' => 2018, 'week' => 44))
          assert_equal('Saturday', view_model.get_period_for('day_of_week' => 7))
          assert_equal('2018-4-1', view_model.get_period_for('year' => 2018, 'month' => 4, 'day' => 1))
        end