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

def test_motohawk(self):
        filename = os.path.join('tests', 'files', 'motohawk.dbc')

        with open(filename, 'r') as fin:
            db = cantools.db.load(fin)

        self.assertEqual(len(db.nodes), 2)
        self.assertEqual(db.nodes[0].name, 'PCM1')
        self.assertEqual(db.nodes[1].name, 'FOO')
        self.assertEqual(len(db.messages), 1)
        self.assertEqual(len(db.messages[0].signals[2].receivers), 2)
        self.assertEqual(db.messages[0].signals[2].receivers[0], 'PCM1')
        self.assertEqual(db.messages[0].signals[2].receivers[1], 'FOO')
        self.assertEqual(db.messages[0].signals[1].receivers, [])

        with open(filename, 'rb') as fin:
            self.assertEqual(db.as_dbc_string().encode('ascii'), fin.read())

def test_motohawk(self):
        filename = os.path.join('tests', 'files', 'motohawk.dbc')

        with open(filename, 'r') as fin:
            db = cantools.db.load(fin)

        self.assertEqual(len(db.nodes), 2)
        self.assertEqual(db.nodes[0].name, 'PCM1')
        self.assertEqual(db.nodes[1].name, 'FOO')
        self.assertEqual(len(db.messages), 1)
        self.assertEqual(len(db.messages[0].signals[2].receivers), 2)
        self.assertEqual(db.messages[0].signals[2].receivers[0], 'PCM1')
        self.assertEqual(db.messages[0].signals[2].receivers[1], 'FOO')
        self.assertEqual(db.messages[0].signals[1].receivers, [])

        with open(filename, 'rb') as fin:
            self.assertEqual(db.as_dbc_string().encode('ascii'), fin.read())

def test_get_message_by_frame_id_and_name(self):
        filename = os.path.join('tests', 'files', 'motohawk.dbc')

        with open(filename, 'r') as fin:
            db = cantools.db.load(fin)

        message = db.get_message_by_name('ExampleMessage')
        self.assertEqual(message.name, 'ExampleMessage')

        message = db.get_message_by_frame_id(496)
        self.assertEqual(message.frame_id, 496)

def test_load_bad_format(self):
        with self.assertRaises(cantools.db.UnsupportedDatabaseFormatError):
            cantools.db.load(StringIO(''))

def test_attributes(self):
        filename = os.path.join('tests', 'files', 'attributes.dbc')

        with open(filename, 'r') as fin:
            db = cantools.db.load(fin)

        # Signal attributes.
        attributes = db.messages[0].signals[0].dbc.attributes

        attribute = attributes['TheSignalStringAttribute']
        self.assertEqual(attribute.name, 'TheSignalStringAttribute')
        self.assertEqual(attribute.value, 'TestString')
        self.assertEqual(attribute.definition,
                         db.dbc.attribute_definitions['TheSignalStringAttribute'])
        self.assertEqual(attribute.definition.default_value, '100')
        self.assertEqual(attribute.definition.kind, 'SG_')
        self.assertEqual(attribute.definition.type_name, 'STRING')
        self.assertEqual(attribute.definition.minimum, None)
        self.assertEqual(attribute.definition.maximum, None)
        self.assertEqual(attribute.definition.choices, None)

def test_attributes(self):
        filename = os.path.join('tests', 'files', 'attributes.dbc')

        with open(filename, 'r') as fin:
            db = cantools.db.load(fin)

        # Signal attributes.
        attributes = db.messages[0].signals[0].dbc.attributes

        attribute = attributes['TheSignalStringAttribute']
        self.assertEqual(attribute.name, 'TheSignalStringAttribute')
        self.assertEqual(attribute.value, 'TestString')
        self.assertEqual(attribute.definition,
                         db.dbc.attribute_definitions['TheSignalStringAttribute'])
        self.assertEqual(attribute.definition.default_value, '100')
        self.assertEqual(attribute.definition.kind, 'SG_')
        self.assertEqual(attribute.definition.type_name, 'STRING')
        self.assertEqual(attribute.definition.minimum, None)
        self.assertEqual(attribute.definition.maximum, None)
        self.assertEqual(attribute.definition.choices, None)

def test_setters(self):
        filename = os.path.join('tests', 'files', 'attributes.dbc')

        with open(filename, 'r') as fin:
            db = cantools.db.load(fin)

        # Calling the setters for coverage. Assertions are not
        # necessary here since functionality is trivial.
        db.nodes[0].name = 'SetterName'
        db.nodes[0].comment = 'SetterComment'
        db.dbc.attributes['BusType'].value = 'LIN'
        db.messages[0].name = 'SetterName'
        db.messages[0].frame_id = 0x12121212
        db.messages[0].is_extended_frame = True
        db.messages[0].length = 6
        db.messages[0].comment = 'TheNewComment'
        db.messages[0].bus_name = 'TheNewBusName'
        db.messages[0].signals[0].name = 'SetterName'
        db.messages[0].signals[0].start = 8
        db.messages[0].signals[0].length = 8
        db.messages[0].signals[0].byte_order = 'big_endian'

def test_refresh(self):
        filename = os.path.join('tests', 'files', 'attributes.dbc')

        with open(filename, 'r') as fin:
            db = cantools.db.load(fin)

        message = db.get_message_by_frame_id(0x39)
        self.assertEqual(message.name, 'TheMessage')
        message.frame_id = 0x40
        db.refresh()
        message = db.get_message_by_frame_id(0x40)
        self.assertEqual(message.name, 'TheMessage')
        self.assertEqual(message.frame_id,0x40)

        message.name = 'TheNewMessage'
        db.refresh()
        message = db.get_message_by_name('TheNewMessage')
        self.assertEqual(message.name, 'TheNewMessage')
        self.assertEqual(message.frame_id, 0x40)

        with self.assertRaises(KeyError) as cm:

def test_load_bad_format(self):
        with self.assertRaises(cantools.db.UnsupportedDatabaseFormatError):
            cantools.db.load(StringIO(''))