def check_requirements()

in nox.py [0:0]


def check_requirements(session):
    """Checks for out of date requirements and optionally updates them."""
    session.install('gcp-devrel-py-tools')

    if 'update' in session.posargs:
        command = 'update-requirements'
    else:
        command = 'check-requirements'

    reqfiles = list(_list_files('.', 'requirements*.txt'))

    for reqfile in reqfiles:
        session.run('gcp-devrel-py-tools', command, reqfile)