text: import math
  from decimal import Decimal
  
  from djmodels.db.models import DecimalField
  from djmodels.db.models.functions import Ln
  from djmodels.test import TestCase
  
  from ..models import DecimalModel, FloatModel, IntegerModel
  
  
  class LnTests(TestCase):
  
      def test_decimal(self):
          DecimalModel.objects.create(n1=Decimal('12.9'), n2=Decimal('0.6'))
          obj = DecimalModel.objects.annotate(n1_ln=Ln('n1'), n2_ln=Ln('n2')).first()
          self.assertIsInstance(obj.n1_ln, Decimal)
          self.assertIsInstance(obj.n2_ln, Decimal)
          self.assertAlmostEqual(obj.n1_ln, Decimal(math.log(obj.n1)))
          self.assertAlmostEqual(obj.n2_ln, Decimal(math.log(obj.n2)))
  
      def test_float(self):
          FloatModel.objects.create(f1=27.5, f2=0.33)
          obj = FloatModel.objects.annotate(f1_ln=Ln('f1'), f2_ln=Ln('f2')).first()
          self.assertIsInstance(obj.f1_ln, float)
          self.assertIsInstance(obj.f2_ln, float)
          self.assertAlmostEqual(obj.f1_ln, math.log(obj.f1))
          self.assertAlmostEqual(obj.f2_ln, math.log(obj.f2))
  
      def test_integer(self):
          IntegerModel.objects.create(small=20, normal=15, big=1)
          obj = IntegerModel.objects.annotate(
              small_ln=Ln('small'),
              normal_ln=Ln('normal'),
              big_ln=Ln('big'),
          ).first()
          self.assertIsInstance(obj.small_ln, float)
          self.assertIsInstance(obj.normal_ln, float)
          self.assertIsInstance(obj.big_ln, float)
          self.assertAlmostEqual(obj.small_ln, math.log(obj.small))
          self.assertAlmostEqual(obj.normal_ln, math.log(obj.normal))
          self.assertAlmostEqual(obj.big_ln, math.log(obj.big))
  
      def test_transform(self):
          try:
              DecimalField.register_lookup(Ln)
              DecimalModel.objects.create(n1=Decimal('12.0'), n2=Decimal('0'))
              DecimalModel.objects.create(n1=Decimal('1.0'), n2=Decimal('0'))
              objs = DecimalModel.objects.filter(n1__ln__gt=0)
              self.assertQuerysetEqual(objs, [Decimal('12.0')], lambda a: a.n1)
          finally:
              DecimalField._unregister_lookup(Ln)
  