8. Plugs Tutorial

About Plugs

Plugs are an OpenHTF concept. The OpenHTF team defines them as follow:

The essence of an OpenHTF test is to interact with a DUT to exercise it in various ways and observe the result. Sometimes this is done by communicating directly with the DUT, and other times it’s done by communicating with a piece of test equipment to which the DUT is attached in some way. A plug is a piece of code written to enable OpenHTF to interact with a particular type of hardware, whether that be a DUT itself or a piece of test equipment.

Technically, plugs are a Python class that is instanciated once per test and shared between test phases. They have a strong sense of cleanup that allows them to execute specific teardown actions regardless of the test outcome.

Although OpenHTF references hardware directly, plugs are also used in various roles that are non-related to hardware, such as user input. Overall, a better explanation would be that they are used for resources that are shared by test cases:

  • Plugs for test equipments

  • Plugs for DUT interfacing, which can be subdivised in some cases:

    • COM Interface

    • SSH Interface

    • Etc.

  • Plugs for user input

  • Plugs for custom frontend interaction

  • Plugs for sharing test context, such as calibration performed over multiple test cases

Using Plugs

Using plugs in spintop-openhtf is pretty straightforward. Let’s take the UserInput plug as example since it is used in pretty much all tests.

  1. First, the plug must be imported.

    from openhtf.plugs.user_input import UserInput
  2. Then, on testcases that require this plug, the plug decorator must be used.

    from openhtf.plugs.user_input import UserInput
    from spintop_openhtf import TestPlan
    plan = TestPlan('mytest')
    @plan.plug(prompt=UserInput) # 'prompt' is user-defined
    def test_1(test, prompt): # prompt will contain an instance of UserInput

The class of the plug is used as argument to the plug decorator. This is important. The executor will instantiate an instance of the class and use the same object across a test run. On each new test, the plug will be re-instantiated.


You choose the name you want to give to the argument. The name must have a match in the function definition. For example, the following would FAIL:

# Will complain that 'prompt' is not an argument
def test_1(test, user_input): # WRONG. No user_input argument exists

Creating Plugs

Creating plugs is the basis of reusing interface functionnalities. As an example, we will create a plug that copies a file from a source folder to a destination.

Base Structure

Every plug must inherit from BasePlug. Moreover, the __init__ method must take no arguments. The following excerpt illustrates the plug definition

import shutil

from openhtf.plugs import BasePlug

class FileCopier(BasePlug):
    def copy_file(self, source_file, destination_folder):
        shutil.copy(source_file, destination_folder)

The following excerpt instanciates the plug in a test case.

@plan.testcase('File Copy Test')
def file_copy_test(test, copy_plug):
    copy_plug.copy_file(source, destination)

Tutorial source

Wrapping spintop-openhtf Plugs

A typical manner of creating custom plugs for a test bench is to wrap an existing, spintop-openhtf plug, to add applicative functionalities to it.

For example, a linux shell plug specific to a product can be created by wrapping the spintop-openhtf comport plug. The plug adds typical linux features to the comport plug such as login, file read, file copy, etc.

The plug is created

from spintop_openhtf.plugs.iointerface.comport import ComportInterface

class LinuxPlug(ComportInterface):

    def __init__(self, comport, baudrate=115200):
        super().__init__(comport, baudrate)

    def login(self, username):
        return self.com_target("{}".format(username), '{}@'.format(username), timeout=10, keeplines=0)

    def file_read(self, file):
        return self.com_target("cat {}".format(file), '@', timeout=10, keeplines=0)

    def file_copy(self, source, destination):
        return self.com_target("cp {} {}".format(source, destination), '@', timeout=10, keeplines=0)

and imported in a test case

linux_plug = LinuxPlug.as_plug( 'linux_plug', comport='COM5',  baudrate=115200)

def LinuxTest(test, linux):
        test.logger.info ("COM Port open")
        test.logger.info ("COM Port open failed")
        return PhaseResult.STOP