def when_no_output(): expect(get_version('echo', argument='')) == ""
def with_no_argument(): expect(get_version('pip', argument='')).contains("Usage:")
def when_found(): expect(get_version('python')).contains("Python ")
def with_custom_argument(): expect(get_version('python', argument='-V')).contains("Python ")
def when_missing(): expect(get_version('foobar')) == "sh: command not found: foobar"