new_contents: from django.test import SimpleTestCase
  
  from corehq.apps.userreports.reports.builder import const
  from corehq.apps.userreports.reports.builder.filter_formats import get_pre_filter_format
  
  
  class PreFilterFormatTest(SimpleTestCase):
  
      def test_empty_filter_format(self):
          self.assertEqual(const.PRE_FILTER_VALUE_IS_EMPTY, get_pre_filter_format({
              'pre_operator': '',
              'pre_value': '',
          }))
  
      def test_exists_filter_format(self):
          self.assertEqual(const.PRE_FILTER_VALUE_EXISTS, get_pre_filter_format({
              'pre_operator': '!=',
              'pre_value': '',
          }))
  
      def test_not_equal_filter_format(self):
          self.assertEqual(const.PRE_FILTER_VALUE_NOT_EQUAL, get_pre_filter_format({
              'pre_operator': 'distinct from',
              'pre_value': '',
          }))
          self.assertEqual(const.PRE_FILTER_VALUE_NOT_EQUAL, get_pre_filter_format({
              'pre_operator': 'distinct from',
              'pre_value': 'a_value',
          }))
  
      def test_value_filter_format(self):
          self.assertEqual(const.FORMAT_VALUE, get_pre_filter_format({
              'pre_operator': '=',
              'pre_value': 'a_value',
          }))
  
      def test_date_filter_format(self):
          # this is a bit weird but just documenting current behavior, which uses
          # the lack of value to assume it is a date
          self.assertEqual(const.FORMAT_DATE, get_pre_filter_format({
              'pre_operator': '=',
              'pre_value': '',
          }))
  
subject: add tests for get_pre_filter_format