Subject: Re: [PATCH net-next v2 03/12] selftests: net: py: add test variants

From: Petr Machata <[email-masked]>
Date: Wed, 19 Nov 2025 15:42:39 +0100

Jakub Kicinski <[email-masked]> writes:

> diff --git a/tools/testing/selftests/net/lib/py/ksft.py b/tools/testing/selftests/net/lib/py/ksft.py
> index 52c42c313cf2..47e0af210bee 100644
> --- a/tools/testing/selftests/net/lib/py/ksft.py
> +++ b/tools/testing/selftests/net/lib/py/ksft.py
> @@ -185,6 +185,49 @@ KSFT_DISRUPTIVE = True
>      return wrapper
>  
>  
> +class KsftNamedVariant:
> +    """ Named string name + argument list tuple for @ksft_variants """
> +
> +    def __init__(self, name, *params):
> +        self.params = params
> +        self.name = name or "_".join([str(x) for x in self.params])
> +
> +
> +def ksft_variants(params):
> +    """
> +    Decorator defining the sets of inputs for a test.
> +    The parameters will be included in the name of the resulting sub-case.
> +    Parameters can be either single object, tuple or a KsftNamedVariant.
> +    The argument can be a list or a generator.
> +
> +    Example:
> +
> +    @ksft_variants([
> +        (1, "a"),
> +        (2, "b"),
> +        KsftNamedVariant("three", 3, "c"),
> +    ])
> +    def my_case(cfg, a, b):
> +        pass # ...
> +
> +    ksft_run(cases=[my_case], args=(cfg, ))
> +
> +    Will generate cases:
> +        my_case.1_a
> +        my_case.2_b
> +        my_case.three
> +    """
> +
> +    def decorator(func):
> +        @functools.wraps(func)
> +        def wrapper():
> +            return func
> +        wrapper.ksft_variants = params
> +        wrapper.original_func = func
> +        return wrapper
> +    return decorator

This uses the wrapper() merely as a vessel to carry the three
attributes. I think the idea would be better expressed as a namedtupple

    from collections import namedtuple

    KsftCaseFunction = namedtuple("KsftCaseFunction",
                                  ['name', 'original_func', 'variants'])

    def ksft_variants(params):
        return lambda func: KsftCaseFunction(func.__name__, func, params)

> +
> +
>  def ksft_setup(env):
>      """
>      Setup test framework global state from the environment.
> @@ -236,7 +279,19 @@ KSFT_DISRUPTIVE = True
>                      break
>  
>      for func in cases:
> -        test_cases.append((func, args, func.__name__))
> +        if hasattr(func, 'ksft_variants'):

Then this could just be if callable(func) just call it, else the complex
processing.

I'm not married to the namedtuple idea, but I consider using a function
as essentially a struct wrong. It should be a general object.

> +            # Parametrized test - create case for each param
> +            for param in func.ksft_variants:
> +                if not isinstance(param, KsftNamedVariant):
> +                    if not isinstance(param, tuple):
> +                        param = (param, )
> +                    param = KsftNamedVariant(None, *param)
> +
> +                test_cases.append((func.original_func,
> +                                   (*args, *param.params),
> +                                   func.__name__ + "." + param.name))
> +        else:
> +            test_cases.append((func, args, func.__name__))
>  
>      return test_cases