text: import copy
  import unittest
  from contextlib import contextmanager
  
  from django.db import DEFAULT_DB_ALIAS, connection, connections
  from django.db.backends.base.creation import (
      TEST_DATABASE_PREFIX, BaseDatabaseCreation,
  )
  from django.db.backends.postgresql.creation import DatabaseCreation
  from django.test import SimpleTestCase
  
  
  class TestDbSignatureTests(SimpleTestCase):
  
      def get_connection_copy(self):
          # Get a copy of the default connection. (Can't use django.db.connection
          # because it'll modify the default connection itself.)
          test_connection = copy.copy(connections[DEFAULT_DB_ALIAS])
          test_connection.settings_dict = copy.copy(connections[DEFAULT_DB_ALIAS].settings_dict)
          return test_connection
  
      def test_default_name(self):
          # A test db name isn't set.
          prod_name = 'hodor'
          test_connection = self.get_connection_copy()
          test_connection.settings_dict['NAME'] = prod_name
          test_connection.settings_dict['TEST'] = {'NAME': None}
          signature = BaseDatabaseCreation(test_connection).test_db_signature()
          self.assertEqual(signature[3], TEST_DATABASE_PREFIX + prod_name)
  
      def test_custom_test_name(self):
          # A regular test db name is set.
          test_name = 'hodor'
          test_connection = self.get_connection_copy()
          test_connection.settings_dict['TEST'] = {'NAME': test_name}
          signature = BaseDatabaseCreation(test_connection).test_db_signature()
          self.assertEqual(signature[3], test_name)
  
      def test_custom_test_name_with_test_prefix(self):
          # A test db name prefixed with TEST_DATABASE_PREFIX is set.
          test_name = TEST_DATABASE_PREFIX + 'hodor'
          test_connection = self.get_connection_copy()
          test_connection.settings_dict['TEST'] = {'NAME': test_name}
          signature = BaseDatabaseCreation(test_connection).test_db_signature()
          self.assertEqual(signature[3], test_name)
  
  
  @unittest.skipUnless(connection.vendor == 'postgresql', "PostgreSQL-specific tests")
  class PostgreSQLDatabaseCreationTests(SimpleTestCase):
  
      @contextmanager
      def changed_test_settings(self, **kwargs):
          settings = connection.settings_dict['TEST']
          saved_values = {}
          for name in kwargs:
              if name in settings:
                  saved_values[name] = settings[name]
  
          for name, value in kwargs.items():
              settings[name] = value
          try:
              yield
          finally:
              for name, value in kwargs.items():
                  if name in saved_values:
                      settings[name] = saved_values[name]
                  else:
                      del settings[name]
  
      def check_sql_table_creation_suffix(self, settings, expected):
          with self.changed_test_settings(**settings):
              creation = DatabaseCreation(connection)
              suffix = creation.sql_table_creation_suffix()
              self.assertEqual(suffix, expected)
  
      def test_sql_table_creation_suffix_with_none_settings(self):
          settings = dict(CHARSET=None, TEMPLATE=None)
          self.check_sql_table_creation_suffix(settings, "")
  
      def test_sql_table_creation_suffix_with_encoding(self):
          settings = dict(CHARSET='UTF8')
          self.check_sql_table_creation_suffix(settings, "WITH ENCODING 'UTF8'")
  
      def test_sql_table_creation_suffix_with_template(self):
          settings = dict(TEMPLATE='template0')
          self.check_sql_table_creation_suffix(settings, 'WITH TEMPLATE "template0"')
  
      def test_sql_table_creation_suffix_with_encoding_and_template(self):
          settings = dict(CHARSET='UTF8', TEMPLATE='template0')
          self.check_sql_table_creation_suffix(settings, '''WITH ENCODING 'UTF8' TEMPLATE "template0"''')
  