reveal anything on Linux, at least.
echo 'ls' | TERM=dumb whatnow -noedit -prompt '' 2> "$actualerr" | \
sort > "$actual"
+check "$expectederr" "$actualerr" 'keep first'
+check "$expected" "$actual" 'keep first'
+
+# Check with SHELL unset. system () on Linux (glibc) seems to
+# always use /bin/sh, so this test won't reveal anything with it.
+unset SHELL
+
+echo 'ls' | TERM=dumb whatnow -noedit -prompt '' 2> "$actualerr" | \
+ sort > "$actual"
+
check "$expectederr" "$actualerr"
check "$expected" "$actual"