$* testscript <'cmd $@' >"cmd 1"     # id-testscript
$* foo.test   <'cmd $@' >"cmd foo/1" # id

wd = [dir_path] $build.work
wd += test
wd += 1
$* testscript <'cmd $~' >"cmd $wd"   # wd-testscript

# @@ TMP wd1
#
wd1 = [dir_path] $build.work
wd1 += test
wd1 += foo
wd1 += 1
$* foo.test   <'cmd $~' >"cmd $wd1"   # wd