Add spec for Command::spawn calling back only once
Add spec for Command::spawn calling back only once

Signed-off-by: Katrina Uychaco <ef0b2ab5bd1ac851826b76acd653f3c4825374fb@github.com>

Nikpolik/apm,atom/apm,bronson/apm,bronson/apm,atom/apm,bronson/apm,Nikpolik/apm,Nikpolik/apm,atom/apm,bronson/apm,atom/apm,Nikpolik/apm