How to write test scripts in Python

1. Introduction to the tool library

1.1 python-can

Positioning: A common CAN bus communication library that supports multiple hardware interfaces (SocketCAN, PCAN, Kvaser, etc.).

Core functions:

Connect to a physical CAN device or a virtual interface.

Send/receive CAN messages (standard frame, extended frame).

Supports CAN FD (flexible data rate).

Applicable scenarios: Quickly build a CAN communication prototype, strong compatibility.

1.2 canard (CAN protocol stack)

Positioning: A library focusing on parsing high-level protocols such as UDS (ISO 14229) and J1939.

Core functions:

Parses DBC files and automatically generates signal values.

Supports UDS diagnostic services (such as 0x22 reading data and 0x2E writing data).

Handles multi-frame transmissions (such as the ISO-TP protocol).

Applicable scenarios: Automated testing of diagnostic interaction with the ECU is required.

2. Environmental preparation

2.1 Installation library

# Install the universal CAN librarypip install python-can

# Install canard (UDS protocol support)pip install canard

2.2 Hardware preparation

Physical equipment: PCAN-USB, Kvaser, Vector equipment (relevant driver needs to be installed).

Virtual Testing: Use socketcan (Linux Virtual CAN interface) or CANoe to simulate the bus.

3. Core function implementation examples

3.1 Send and receive CAN messages using python-can

import can

# Connect to the CAN interface (taking socketcan as an example)bus = (channel='vcan0', bustype='socketcan')

# Send single frame datamsg = (
    arbitration_id=0x123,  # CAN ID
    data=[0x01, 0x02, 0x03, 0x04],
    is_extended_id=False    # Standard frame)
(msg)

# Receive datafor msg in bus:
    print(f"Received: ID={hex(msg.arbitration_id)}, Data={}")

# Close the connection()

3.2 Use canard to parse DBC files

from canard import Canard
from  import socketcan

# Load DBC filedbc = Canard()
dbc.load_dbc('')

# Create a virtual CAN interfacedev = ('vcan0')
()

# parse received messagesdef on_message(msg):
    decoded = dbc.decode_message(msg.arbitration_id, )
    print(f"Signal value: {decoded}")

dev.add_listener(on_message)

3.3 Implementing UDS diagnostic service (based on canard)

from  import UdsClient

# Create a UDS clientuds = UdsClient(transport=(bustype='socketcan', channel='vcan0'))

# Send diagnostic request: read the ECU serial number (service 0x22, parameter 0xF189)response = ([0x22, 0xF1, 0x89])
if response:
    print(f"ECU Serial number: {bytes([2:]).decode()}")
else:
    print("Request timeout")

4. Automated test script design

4.1 Test scenario example: Door status verification

def test_door_status():
    bus = (channel='vcan0', bustype='socketcan')
    
    # Send door control command (ID=0x200, data=[0x01] indicates door opening)    ((arbitration_id=0x200, data=[0x01]))
    
    # Wait and verify door status feedback (expected ID=0x201, data[0]=0x01)    for msg in bus:
        if msg.arbitration_id == 0x201:
            assert [0] == 0x01, "The door is not opened correctly"
            break
    ()

4.2 Integrated testing framework (such as pytest)

import pytest

@
def can_bus():
    bus = (channel='vcan0', bustype='socketcan')
    yield bus
    ()

def test_engine_rpm(can_bus):
    # Send speed request command    can_bus.send((arbitration_id=0x700, data=[0x03]))
    
    # Verify that the response is within a reasonable range (such as 800-5000 RPM)    for msg in can_bus:
        if msg.arbitration_id == 0x701:
            rpm = int.from_bytes([2:4], byteorder='big')
            assert 800 &lt;= rpm &lt;= 5000, "Abnormal speed"
            break

5. Advanced application skills

5.1 CAN FD Support

# Use python-can to send CAN FD messagesmsg = (
    arbitration_id=0x123,
    data=[i % 256 for i in range(64)],  # 64 bytes of data    is_fd=True,
    bitrate_switch=True  # Enable bit rate switching)
(msg)

5.2 Integration with HIL system

# Connect Vector hardware (with XL Driver required)bus = (
    bustype='vector',
    channel=1,
    app_name='Python_HIL_Test'
)

# Send synchronous periodic messagestask = bus.send_periodic(msgs=[msg1, msg2], period=0.1)
()  # Stop sending

5.3 Automated test report generation

# Use pytest-html to generate a test report(["--html="])

6. FAQs and debugging

6.1 Hardware connection failed

Phenomenon: CanError: Error sending message

solve:

Check whether the device driver is installed (such as PCAN-Basic API required).

Confirm channel permissions (Linux requires sudo ip link set vcan0 up).

6.2 DBC parsing error

Phenomenon: KeyError: 'Unknown frame ID'

Solution: Make sure the DBC file contains the definition of the target CAN ID.

6.3 Multi-frame transmission processing

# Use canard to handle ISO-TP multi-frame transmissionfrom .iso_tp import IsoTpTransport

tp = IsoTpTransport(can_bus, tx_id=0x7E0, rx_id=0x7E8)
data = ()  # Receive long data（Automatic reorganization）

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