def get_and_check_wine_arch_valid(wine_arch: str = '') -> str:
    """
    check for valid winearch - if wine_arch is empty, default to win32
    valid choices: win32, win64

    >>> import unittest
    >>> assert get_and_check_wine_arch_valid() == 'win32'
    >>> assert get_and_check_wine_arch_valid('win32') == 'win32'
    >>> assert get_and_check_wine_arch_valid('win64') == 'win64'
    >>> unittest.TestCase().assertRaises(RuntimeError, get_and_check_wine_arch_valid, wine_arch='invalid')
    """
    valid_wine_archs = ['win32', 'win64']
    if not wine_arch:
        wine_arch = 'win32'
    wine_arch = wine_arch.lower().strip()
    if wine_arch not in valid_wine_archs:
        raise RuntimeError('Invalid wine_arch: "{wine_arch}"'.format(wine_arch=wine_arch))
    return wine_arch