root:
             product   file:plan.py
             product   step:./plan.py

file:plan.py
               state = CONFIRMED
             creator   root:
                sink   step:./plan.py

step:./plan.py
               state = FAILED
                need = PLAN
           using_env = STEPUP_PATH_FILTER [dynamic]
             creator   root:
              source   file:plan.py
             product   file:work.py

file:work.py
               state = CONFIRMED
             creator   step:./plan.py
                sink   (step:./work.py)

(step:./work.py)
               state = SUCCEEDED
                need = DEFAULT
           using_env = STEPUP_PATH_FILTER [dynamic]
              source   file:work.py
