old_contents: from click.exceptions import BadParameter
  import pytest
  
  from djclick import params
  
  
  @pytest.mark.django_db
  def test_modelinstance_init():
      from testapp.models import DummyModel
      from django.db.models.query import QuerySet
  
      param = params.ModelInstance(DummyModel)
      assert isinstance(param.qs, QuerySet)
  
      qs = DummyModel.objects.all()
      param = params.ModelInstance(qs)
      assert param.qs is qs
  
  
  @pytest.mark.django_db
  @pytest.mark.parametrize(
      ('arg', 'value'),
      (
          ('--pk', '1'),
          ('--slug', 'test'),
          ('--endswith', 'st'),
      )
  )
  def test_convert_ok(call_command, arg, value):
      from testapp.models import DummyModel
  
      DummyModel.objects.create(pk=1, slug='test')
      expected = b'<DummyModel: 1>'
  
      assert call_command('modelcmd', arg, value).stdout == expected
  
  
  @pytest.mark.django_db
  @pytest.mark.parametrize(
      ('args', 'error_message'),
      (
          (('--pk', '99'), "pk=99"),
          (('--slug', 'doesnotexist'), "slug=doesnotexist"),
      )
  )
  def test_convert_fail(call_command, args, error_message):
      with pytest.raises(BadParameter) as e:
          call_command('modelcmd', *args)
      # Use `.endswith()` because of differences between CPython and pypy
      assert str(e).endswith(
          'BadParameter: could not find testapp.DummyModel with {}'.format(
              error_message))
  
new_contents: from click.exceptions import BadParameter
  import pytest
  
  from djclick import params
  
  
  @pytest.mark.django_db
  def test_modelinstance_init():
      from testapp.models import DummyModel
      from django.db.models.query import QuerySet
  
      param = params.ModelInstance(DummyModel)
      assert isinstance(param.qs, QuerySet)
  
      qs = DummyModel.objects.all()
      param = params.ModelInstance(qs)
      assert param.qs is qs
  
  
  @pytest.mark.django_db
  @pytest.mark.parametrize(
      ('arg', 'value'),
      (
          ('--pk', '1'),
          ('--slug', 'test'),
          ('--endswith', 'st'),
      )
  )
  def test_convert_ok(call_command, arg, value):
      from testapp.models import DummyModel
  
      DummyModel.objects.create(pk=1, slug='test')
      expected = b'<DummyModel: 1>'
  
      assert call_command('modelcmd', arg, value).stdout == expected
  
  
  @pytest.mark.django_db
  @pytest.mark.parametrize(
      ('args', 'error_message'),
      (
          (('--pk', '99'), "pk=99"),
          (('--slug', 'doesnotexist'), "slug=doesnotexist"),
      )
  )
  def test_convert_fail(call_command, args, error_message):
      with pytest.raises(BadParameter) as e:
          call_command('modelcmd', *args)
      assert e.match(
          'could not find testapp.DummyModel with {}'.format(error_message))
  
subject: Fix a check for specific formatting of an error message