How to use the cantools.db.load_string function in cantools

self.assertEqual(
            str(cm.exception),
            'Invalid syntax at line 2, column 19: "BO_ 546 EMV_Stati '
            '>>!<<8 EMV_Statusmeldungen"')

        # Missing frame id in message comment.
        with self.assertRaises(textparser.ParseError) as cm:
            cantools.db.formats.dbc.load_string('CM_ BO_ "Foo.";')

        self.assertEqual(
            str(cm.exception),
            'Invalid syntax at line 1, column 9: "CM_ BO_ >>!<<"Foo.";"')

        # Missing frame id in message comment, using load_string().
        with self.assertRaises(cantools.db.UnsupportedDatabaseFormatError) as cm:
            cantools.db.load_string('CM_ BO_ "Foo.";')

        self.assertEqual(
            str(cm.exception),
            "DBC: \"Invalid syntax at line 1, column 9: \"CM_ BO_ >>!<<\"Foo."
            "\";\"\", KCD: \"syntax error: line 1, column 0\", SYM: \"Only SYM "

def test_invalid_kcd(self):
        with self.assertRaises(cantools.db.UnsupportedDatabaseFormatError) as cm:
            cantools.db.load_string('',
                                    database_format='kcd')

        self.assertEqual(
            str(cm.exception),
            'KCD: "Expected root element tag '
            '{http://kayak.2codeornot2code.org/1.0}NetworkDefinition, but '

def test_invalid_kcd(self):
        with self.assertRaises(cantools.db.UnsupportedDatabaseFormatError) as cm:
            cantools.db.load_string('',
                                    database_format='kcd')

        self.assertEqual(
            str(cm.exception),
            'KCD: "Expected root element tag '
            '{http://kayak.2codeornot2code.org/1.0}NetworkDefinition, but '

self.assertEqual(
            str(cm.exception),
            'Invalid syntax at line 2, column 19: "BO_ 546 EMV_Stati '
            '>>!<<8 EMV_Statusmeldungen"')

        # Missing frame id in message comment.
        with self.assertRaises(textparser.ParseError) as cm:
            cantools.db.formats.dbc.load_string('CM_ BO_ "Foo.";')

        self.assertEqual(
            str(cm.exception),
            'Invalid syntax at line 1, column 9: "CM_ BO_ >>!<<"Foo.";"')

        # Missing frame id in message comment, using load_string().
        with self.assertRaises(cantools.db.UnsupportedDatabaseFormatError) as cm:
            cantools.db.load_string('CM_ BO_ "Foo.";')

        self.assertEqual(
            str(cm.exception),
            "DBC: \"Invalid syntax at line 1, column 9: \"CM_ BO_ >>!<<\"Foo."
            "\";\"\", KCD: \"syntax error: line 1, column 0\", SYM: \"Only SYM "

def test_extended_id_dump(self):
        filename = os.path.join('tests', 'files', 'test_extended_id_dump.dbc')
        db = cantools.db.load_file(filename)
        dumped_db = cantools.db.load_string(db.as_dbc_string())
        reg_id_msg = dumped_db.get_message_by_frame_id(0x100)
        ext_id_msg = dumped_db.get_message_by_frame_id(0x1c2a2a2a)

        self.assertEqual(reg_id_msg.is_extended_frame, False)
        self.assertEqual(ext_id_msg.is_extended_frame, True)

def test_string_attribute_definition_dump(self):
        filename = os.path.join('tests', 'files', 'test_multiplex_dump.dbc')
        db = cantools.db.load_file(filename)
        dumped_db = cantools.db.load_string(db.as_dbc_string())
        attribute = dumped_db.dbc.attribute_definitions

        self.assertEqual(attribute['BusType'].type_name, "STRING")

def test_string_attribute_definition_dump(self):
        filename = os.path.join('tests', 'files', 'test_multiplex_dump.dbc')
        db = cantools.db.load_file(filename)
        dumped_db = cantools.db.load_string(db.as_dbc_string())
        attribute = dumped_db.dbc.attribute_definitions

        self.assertEqual(attribute['BusType'].type_name, "STRING")

def test_multiplex_dump(self):
        filename = os.path.join('tests', 'files', 'test_multiplex_dump.dbc')
        db = cantools.db.load_file(filename)
        dumped_db = cantools.db.load_string(db.as_dbc_string())
        dumped_msg = dumped_db.get_message_by_frame_id(0x100)

        self.assertEqual(dumped_msg.signals[0].name, "MultiplexorSig")
        self.assertEqual(dumped_msg.signals[0].is_multiplexer, True)
        self.assertEqual(dumped_msg.signals[0].multiplexer_ids, None)
        self.assertEqual(dumped_msg.signals[1].name, "MultiplexedSig")
        self.assertEqual(dumped_msg.signals[1].is_multiplexer, False)
        self.assertEqual(dumped_msg.signals[1].multiplexer_ids[0], 0x2a)
        self.assertEqual(dumped_msg.signals[2].name, "UnmultiplexedSig")
        self.assertEqual(dumped_msg.signals[2].multiplexer_ids, None)
        self.assertEqual(dumped_msg.signals[2].is_multiplexer, False)

def test_multiplex_dump(self):
        filename = os.path.join('tests', 'files', 'test_multiplex_dump.dbc')
        db = cantools.db.load_file(filename)
        dumped_db = cantools.db.load_string(db.as_dbc_string())
        dumped_msg = dumped_db.get_message_by_frame_id(0x100)

        self.assertEqual(dumped_msg.signals[0].name, "MultiplexorSig")
        self.assertEqual(dumped_msg.signals[0].is_multiplexer, True)
        self.assertEqual(dumped_msg.signals[0].multiplexer_ids, None)
        self.assertEqual(dumped_msg.signals[1].name, "MultiplexedSig")
        self.assertEqual(dumped_msg.signals[1].is_multiplexer, False)
        self.assertEqual(dumped_msg.signals[1].multiplexer_ids[0], 0x2a)
        self.assertEqual(dumped_msg.signals[2].name, "UnmultiplexedSig")
        self.assertEqual(dumped_msg.signals[2].multiplexer_ids, None)
        self.assertEqual(dumped_msg.signals[2].is_multiplexer, False)