Plugs: Hardware and Instrument Abstraction

Discover how to use OpenHTF's plugin system to abstract hardware interactions and encapsulate reusable test logic with examples.

Manage external hardware and resources with reusable logic.

Test start
__init__()plug instantiated
phase_test(test, multimeter)multimeter.measure_voltage()
tearDown()resources released
Test end

MultimeterPlug

idle

self.logger

Hardware tests often require connections to external resources like instruments, UUTs, or other softwares. OpenHTF manages these connections through Plugs, reusable classes that handle resource initialization, control, and cleanup, separating test logic from resource management for easier maintenance and better logging.

Syntax

A plug is a standard Python class that inherits from BasePlug.

multimeter_plug.py

from openhtf import plugs
import random

class MultimeterPlug(plugs.BasePlug):
    def __init__(self):
        # Simulate connecting to the multimeter
        self.connected = True

    def tearDown(self):
        # Automatically called by OpenHTF after the test to clean up
        self.connected = False

    def measure_voltage(self):
        # Simulate voltage measurement
        return random.uniform(0, 10)

    def measure_current(self):
        # Simulate current measurement
        return random.uniform(0, 2)

Usage

You can then use the plug decorator in your test phases to inject the plug.

main.py

import openhtf as htf
from multimeter_plug import MultimeterPlug

@htf.plug(multimeter=MultimeterPlug)
def phase_test(test, multimeter):
    # Use the plug to measure voltage and current
    voltage = multimeter.measure_voltage()
    current = multimeter.measure_current()

def main():
    test = htf.Test(phase_test)
    test.execute(lambda: "SN1234")

if __name__ == "__main__":
    main()

Hardware you connect this way — a multimeter over SCPI, a DUT over a serial port, a PLC over Modbus — has a dedicated guide: PyVISA, pyserial, pymodbus. OpenHTF also ships ready-made plugs for ADB, Fastboot and serial capture.

OpenHTF manages the plug's lifecycle automatically:

Instantiation: At the start of the test, OpenHTF instantiates the plug by calling its __init__() method.
Logging: During the test, the plug can log important actions or events using self.logger.
Teardown: After the test concludes, OpenHTF automatically calls the tearDown() method to clean up resources. This ensures reliable cleanup since Python's destructors __del__() aren't always called.

User Input Plug

You can use the UserInput plug to prompt the operator during the test. The text_input parameter controls the type of interaction - when missing, it defaults to False (button prompt).

messagestr

Text shown to the operator, in the console and in the Operator UI.

text_inputbool

True renders a text field; False (default) renders an Okay button.

timeout_sfloat or None

Raise PromptUnansweredError if the operator does not answer in time. Default: wait forever.

image_urlstr or None

URL of an image to show above the prompt in the Operator UI — a photo of the connector to plug, the LED to check. Ignored on the console.

cli_colorstr

ANSI color code for the console prompt (e.g. colorama.Fore.CYAN).

main.py

import openhtf as htf
from openhtf.plugs.user_input import UserInput

@htf.measures(
    htf.Measurement("led_color")
    .with_validator(lambda color: color in ["Red", "Green", "Blue"])
)
@htf.plug(user_input=UserInput)
def prompt_operator_led_color(test, user_input):
    # text_input defaults to False when not specified
    led_color = user_input.prompt(
        message="What is the LED color? (Red/Green/Blue)",
        text_input=True  # Explicitly set to True for text input
    )
    test.measurements.led_color = led_color

def main():
    test = htf.Test(prompt_operator_led_color)
    test.execute(lambda: "SN1234")

if __name__ == "__main__":
    main()

Text Input vs Button Prompts

The text_input parameter determines the prompt behavior:

text_input=True: Displays a text input field where the operator types a response
text_input=False (default): Displays a button prompt where the operator clicks "Okay"

Text Input Example

# Text input prompt - operator types response
response = user_input.prompt(
    message="What is the LED color? (Red/Green/Blue)",
    text_input=True
)

Button Prompt Example

# Button prompt - operator clicks "Okay" (text_input defaults to False)
user_input.prompt(
    message="Click Okay when the LED turns on"
)

Terminal

What is the LED color? (Red/Green/Blue):
--> Red

======================= test: openhtf_test  outcome: PASS ======================

Advanced use cases

Single plug configuration

You can define and load configurations specific to a plug, similar to test configurations.

multimeter_plug.py

from openhtf import BasePlug
from openhtf.util.configuration import CONF

# Define `com_port` configuration
CONF.declare("com_port", default_value="COM1")

class MultimeterPlug(BasePlug):
    # Simulate connecting to the multimeter
    def __init__(self):
        self.com_port = CONF.com_port
        self.connected = True

    # Simulate measuring the voltage
    def measure_voltage(self):
        return 3.3

    # Simulate disconnecting from the multimeter
    # This method is called automatically by OpenHTF at the end of the test
    def tearDown(self):
        self.connected = False

Multiple plug configuration

You can use bind_init_args to create multiple plug instances with variable configurations. This ensures flexible plug setup while maintaining compatibility with OpenHTF's automatic plug lifecycle management.

multimeter_plug.py

from openhtf import BasePlug

class MultimeterPlug(BasePlug):
    # Simulate connecting to the multimeter with port argument
    def __init__(self, com_port: str):
        self.com_port = com_port
        self.connected = True

    # Simulate measuring the voltage
    def measure_voltage(self):
        return 3.3

    # Simulate disconnecting from the multimeter
    # This method is called automatically by OpenHTF at the end of the test
    def tearDown(self):
        self.connected = False

main.py

import openhtf as htf
from openhtf.plugs import plug
from openhtf.util.configuration import CONF, bind_init_args
from multimeter_plug import MultimeterPlug

COM_PORT_1 = CONF.declare("com_port_1", default_value="COM1")
COM_PORT_2 = CONF.declare("com_port_2", default_value="COM2")

MultimeterPlug1 = bind_init_args(MultimeterPlug, COM_PORT_1)
MultimeterPlug2 = bind_init_args(MultimeterPlug, COM_PORT_2)

@plug(multimeter=MultimeterPlug1)
def test_voltage_1(test, multimeter):
    multimeter.measure_voltage()

@plug(multimeter=MultimeterPlug2)
def test_voltage_2(test, multimeter):
    multimeter.measure_voltage()

def main():
    test = htf.Test(test_voltage_1, test_voltage_2)
    test.execute(lambda: "PCB0001")  # UUT S/N

if __name__ == "__main__":
    main()

Plugs

Syntax

Usage

User Input Plug

Text Input vs Button Prompts

Advanced use cases

Single plug configuration

Multiple plug configuration

Building a pyserial plug

Building a PyVISA plug

Bundled plugs

Configuration

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