@task
def test(context):
    context.run('echo 123')

$ inv test
123
sys:1: ResourceWarning: unclosed file <_io.FileIO name=4 mode='wb' closefd=True>
sys:1: ResourceWarning: unclosed file <_io.FileIO name=5 mode='rb' closefd=True>
sys:1: ResourceWarning: unclosed file <_io.FileIO name=7 mode='rb' closefd=True>
$ uname -a
Linux archlinux 5.2.6-arch1-1-ARCH #1 SMP PREEMPT Sun Aug 4 14:58:49 UTC 2019 x86_64 GNU/Linux
$ python --version
Python 3.7.4
$ invoke --version
Invoke 1.3.0