tests require writable ${SRCTOP}/. . . ? (sbin/md5/tests/ example)

Example context:

path: root/sbin/md5/tests/Makefile
with content including:

PACKAGE=		tests

TEST_DIR=		${SRCTOP}/sbin/md5/tests

.PATH:			${TEST_DIR}

. . .

.SUFFIXES:		.SH

.SH.sh:
	sed 's|%%TESTSBASE%%|${TESTSBASE}|g' ${.ALLSRC} > ${.TARGET}

. . .




This left various untracked files in sbin/md5/tests/ in my environment.
(Only noticed later, when looking around. Other files were also left
behind but this is enough of an example to ask the general question.)

Is there an intent to require writable source trees for this snd to leave
behind untracked files in the source tree?

Both main and stable/13 have the property as stands. (I did not check
elsewhere.)

===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)