$ copy-file changes/B.scala B.scala

$ copy-file changes/A1.scala a/A.scala
$ sleep 1000

> run 1
$ copy-file changes/A2.scala a/A.scala
$ sleep 1000

# done this way because last modified times often have ~1s resolution
> run 2
$ copy-file changes/A1.scala a/A.scala
$ sleep 1000

> run 1

$ copy-file changes/A3.scala a/A.scala
$ sleep 1000

> run 3
$ copy-file changes/A1.scala a/A.scala
$ sleep 1000

> run 1
