text: from unittest import mock
  
  from django.apps.registry import Apps
  from django.db import models
  from django.db.models import signals
  from django.dispatch import receiver
  from django.test import TestCase
  from django.test.utils import isolate_apps
  
  from .models import Author, Book, Car, Person
  
  
  class BaseSignalTest(TestCase):
      def setUp(self):
          # Save up the number of connected signals so that we can check at the
          # end that all the signals we register get properly unregistered (#9989)
          self.pre_signals = (
              len(signals.pre_save.receivers),
              len(signals.post_save.receivers),
              len(signals.pre_delete.receivers),
              len(signals.post_delete.receivers),
          )
  
      def tearDown(self):
          # All our signals got disconnected properly.
          post_signals = (
              len(signals.pre_save.receivers),
              len(signals.post_save.receivers),
              len(signals.pre_delete.receivers),
              len(signals.post_delete.receivers),
          )
          self.assertEqual(self.pre_signals, post_signals)
  
  
  class SignalTests(BaseSignalTest):
      def test_model_pre_init_and_post_init(self):
          data = []
  
          def pre_init_callback(sender, args, **kwargs):
              data.append(kwargs['kwargs'])
          signals.pre_init.connect(pre_init_callback)
  
          def post_init_callback(sender, instance, **kwargs):
              data.append(instance)
          signals.post_init.connect(post_init_callback)
  
          p1 = Person(first_name="John", last_name="Doe")
          self.assertEqual(data, [{}, p1])
  
      def test_save_signals(self):
          data = []
  
          def pre_save_handler(signal, sender, instance, **kwargs):
              data.append(
                  (instance, sender, kwargs.get("raw", False))
              )
  
          def post_save_handler(signal, sender, instance, **kwargs):
              data.append(
                  (instance, sender, kwargs.get("created"), kwargs.get("raw", False))
              )
  
          signals.pre_save.connect(pre_save_handler, weak=False)
          signals.post_save.connect(post_save_handler, weak=False)
          try:
              p1 = Person.objects.create(first_name="John", last_name="Smith")
  
              self.assertEqual(data, [
                  (p1, Person, False),
                  (p1, Person, True, False),
              ])
              data[:] = []
  
              p1.first_name = "Tom"
              p1.save()
              self.assertEqual(data, [
                  (p1, Person, False),
                  (p1, Person, False, False),
              ])
              data[:] = []
  
              # Calling an internal method purely so that we can trigger a "raw" save.
              p1.save_base(raw=True)
              self.assertEqual(data, [
                  (p1, Person, True),
                  (p1, Person, False, True),
              ])
              data[:] = []
  
              p2 = Person(first_name="James", last_name="Jones")
              p2.id = 99999
              p2.save()
              self.assertEqual(data, [
                  (p2, Person, False),
                  (p2, Person, True, False),
              ])
              data[:] = []
              p2.id = 99998
              p2.save()
              self.assertEqual(data, [
                  (p2, Person, False),
                  (p2, Person, True, False),
              ])
  
              # The sender should stay the same when using defer().
              data[:] = []
              p3 = Person.objects.defer('first_name').get(pk=p1.pk)
              p3.last_name = 'Reese'
              p3.save()
              self.assertEqual(data, [
                  (p3, Person, False),
                  (p3, Person, False, False),
              ])
          finally:
              signals.pre_save.disconnect(pre_save_handler)
              signals.post_save.disconnect(post_save_handler)
  
      def test_delete_signals(self):
          data = []
  
          def pre_delete_handler(signal, sender, instance, **kwargs):
              data.append(
                  (instance, sender, instance.id is None)
              )
  
          # #8285: signals can be any callable
          class PostDeleteHandler:
              def __init__(self, data):
                  self.data = data
  
              def __call__(self, signal, sender, instance, **kwargs):
                  self.data.append(
                      (instance, sender, instance.id is None)
                  )
          post_delete_handler = PostDeleteHandler(data)
  
          signals.pre_delete.connect(pre_delete_handler, weak=False)
          signals.post_delete.connect(post_delete_handler, weak=False)
          try:
              p1 = Person.objects.create(first_name="John", last_name="Smith")
              p1.delete()
              self.assertEqual(data, [
                  (p1, Person, False),
                  (p1, Person, False),
              ])
              data[:] = []
  
              p2 = Person(first_name="James", last_name="Jones")
              p2.id = 99999
              p2.save()
              p2.id = 99998
              p2.save()
              p2.delete()
              self.assertEqual(data, [
                  (p2, Person, False),
                  (p2, Person, False),
              ])
              data[:] = []
  
              self.assertQuerysetEqual(
                  Person.objects.all(), [
                      "James Jones",
                  ],
                  str
              )
          finally:
              signals.pre_delete.disconnect(pre_delete_handler)
              signals.post_delete.disconnect(post_delete_handler)
  
      def test_decorators(self):
          data = []
  
          @receiver(signals.pre_save, weak=False)
          def decorated_handler(signal, sender, instance, **kwargs):
              data.append(instance)
  
          @receiver(signals.pre_save, sender=Car, weak=False)
          def decorated_handler_with_sender_arg(signal, sender, instance, **kwargs):
              data.append(instance)
  
          try:
              c1 = Car.objects.create(make="Volkswagen", model="Passat")
              self.assertEqual(data, [c1, c1])
          finally:
              signals.pre_save.disconnect(decorated_handler)
              signals.pre_save.disconnect(decorated_handler_with_sender_arg, sender=Car)
  
      def test_save_and_delete_signals_with_m2m(self):
          data = []
  
          def pre_save_handler(signal, sender, instance, **kwargs):
              data.append('pre_save signal, %s' % instance)
              if kwargs.get('raw'):
                  data.append('Is raw')
  
          def post_save_handler(signal, sender, instance, **kwargs):
              data.append('post_save signal, %s' % instance)
              if 'created' in kwargs:
                  if kwargs['created']:
                      data.append('Is created')
                  else:
                      data.append('Is updated')
              if kwargs.get('raw'):
                  data.append('Is raw')
  
          def pre_delete_handler(signal, sender, instance, **kwargs):
              data.append('pre_delete signal, %s' % instance)
              data.append('instance.id is not None: %s' % (instance.id is not None))
  
          def post_delete_handler(signal, sender, instance, **kwargs):
              data.append('post_delete signal, %s' % instance)
              data.append('instance.id is not None: %s' % (instance.id is not None))
  
          signals.pre_save.connect(pre_save_handler, weak=False)
          signals.post_save.connect(post_save_handler, weak=False)
          signals.pre_delete.connect(pre_delete_handler, weak=False)
          signals.post_delete.connect(post_delete_handler, weak=False)
          try:
              a1 = Author.objects.create(name='Neal Stephenson')
              self.assertEqual(data, [
                  "pre_save signal, Neal Stephenson",
                  "post_save signal, Neal Stephenson",
                  "Is created"
              ])
              data[:] = []
  
              b1 = Book.objects.create(name='Snow Crash')
              self.assertEqual(data, [
                  "pre_save signal, Snow Crash",
                  "post_save signal, Snow Crash",
                  "Is created"
              ])
              data[:] = []
  
              # Assigning and removing to/from m2m shouldn't generate an m2m signal.
              b1.authors.set([a1])
              self.assertEqual(data, [])
              b1.authors.set([])
              self.assertEqual(data, [])
          finally:
              signals.pre_save.disconnect(pre_save_handler)
              signals.post_save.disconnect(post_save_handler)
              signals.pre_delete.disconnect(pre_delete_handler)
              signals.post_delete.disconnect(post_delete_handler)
  
      def test_disconnect_in_dispatch(self):
          """
          Signals that disconnect when being called don't mess future
          dispatching.
          """
  
          class Handler:
              def __init__(self, param):
                  self.param = param
                  self._run = False
  
              def __call__(self, signal, sender, **kwargs):
                  self._run = True
                  signal.disconnect(receiver=self, sender=sender)
  
          a, b = Handler(1), Handler(2)
          signals.post_save.connect(a, sender=Person, weak=False)
          signals.post_save.connect(b, sender=Person, weak=False)
          Person.objects.create(first_name='John', last_name='Smith')
  
          self.assertTrue(a._run)
          self.assertTrue(b._run)
          self.assertEqual(signals.post_save.receivers, [])
  
      @mock.patch('weakref.ref')
      def test_lazy_model_signal(self, ref):
          def callback(sender, args, **kwargs):
              pass
          signals.pre_init.connect(callback)
          signals.pre_init.disconnect(callback)
          self.assertTrue(ref.called)
          ref.reset_mock()
  
          signals.pre_init.connect(callback, weak=False)
          signals.pre_init.disconnect(callback)
          ref.assert_not_called()
  
  
  class LazyModelRefTest(BaseSignalTest):
      def setUp(self):
          super().setUp()
          self.received = []
  
      def receiver(self, **kwargs):
          self.received.append(kwargs)
  
      def test_invalid_sender_model_name(self):
          msg = "Invalid model reference 'invalid'. String model references must be of the form 'app_label.ModelName'."
          with self.assertRaisesMessage(ValueError, msg):
              signals.post_init.connect(self.receiver, sender='invalid')
  
      def test_already_loaded_model(self):
          signals.post_init.connect(
              self.receiver, sender='signals.Book', weak=False
          )
          try:
              instance = Book()
              self.assertEqual(self.received, [{
                  'signal': signals.post_init,
                  'sender': Book,
                  'instance': instance
              }])
          finally:
              signals.post_init.disconnect(self.receiver, sender=Book)
  
      @isolate_apps('signals', kwarg_name='apps')
      def test_not_loaded_model(self, apps):
          signals.post_init.connect(
              self.receiver, sender='signals.Created', weak=False, apps=apps
          )
  
          try:
              class Created(models.Model):
                  pass
  
              instance = Created()
              self.assertEqual(self.received, [{
                  'signal': signals.post_init, 'sender': Created, 'instance': instance
              }])
          finally:
              signals.post_init.disconnect(self.receiver, sender=Created)
  
      @isolate_apps('signals', kwarg_name='apps')
      def test_disconnect(self, apps):
          received = []
  
          def receiver(**kwargs):
              received.append(kwargs)
  
          signals.post_init.connect(receiver, sender='signals.Created', apps=apps)
          signals.post_init.disconnect(receiver, sender='signals.Created', apps=apps)
  
          class Created(models.Model):
              pass
  
          Created()
          self.assertEqual(received, [])
  
      def test_register_model_class_senders_immediately(self):
          """
          Model signals registered with model classes as senders don't use the
          Apps.lazy_model_operation() mechanism.
          """
          # Book isn't registered with apps2, so it will linger in
          # apps2._pending_operations if ModelSignal does the wrong thing.
          apps2 = Apps()
          signals.post_init.connect(self.receiver, sender=Book, apps=apps2)
          self.assertEqual(list(apps2._pending_operations), [])
  