old_contents: from datetime import date
  
  from ..period_utils import get_month_shift, get_periods
  
  
  def test_get_month_shift_handles_december():
      new_month, _ = get_month_shift(12, 1)
      assert 12 == new_month
  
  
  def test_get_periods_when_end_date_before_period_end():
      # This should produce eight periods, 2 for each of the years from
      # 2015 to 2018 inclusive
      periods = get_periods(date(2015, 01, 01), date(2018, 12, 31), 1, 2)
      assert 8 == len(periods)
  
new_contents: from datetime import date, timedelta
  
  from ..period_utils import get_month_shift, get_periods, periods_intersect
  
  
  def test_get_month_shift_handles_december():
      new_month, _ = get_month_shift(12, 1)
      assert 12 == new_month
  
  
  def test_get_periods_when_end_date_before_period_end():
      # This should produce eight periods, 2 for each of the years from
      # 2015 to 2018 inclusive
      periods = get_periods(date(2015, 01, 01), date(2018, 12, 31), 1, 2)
      assert 8 == len(periods)
  
  
  def test_periods_instersect_for_no_second_period():
      s = date.today() - timedelta(days=1)
      e = date.today() + timedelta(days=1)
      assert periods_intersect(s, e, None, None)
  
  
  def test_periods_intersect_for_when_second_start_date_less_than_first_end_date():
      s = date.today() - timedelta(days=1)
      e = date.today() + timedelta(days=1)
      x = date.today()
  
      assert periods_intersect(s, e, x, None)
  
  
  def test_periods_intersect_for_when_second_end_date_greater_than_first_start_date():
      s = date.today() - timedelta(days=1)
      e = date.today() + timedelta(days=1)
      y = date.today()
  
      assert periods_intersect(s, e, None, y)
  
  
  def test_periods_intersect_for_when_second_start_date_in_first_period():
      s = date.today() - timedelta(days=1)
      e = date.today() + timedelta(days=1)
      x = date.today()
      y = date.today()
  
      assert periods_intersect(s, e, x, y)
  
  
  def test_periods_intersect_for_when_period_contains_first_period():
      s = date.today() - timedelta(days=1)
      e = date.today() + timedelta(days=1)
      x = date.today() - timedelta(days=2)
      y = date.today() + timedelta(days=2)
  
      assert periods_intersect(s, e, x, y)
  
subject: Add tests for period_intersect logic