test-sysusers: fix how paths are calculated

We were looking at ${f%.*}, i.e. the $f with any suffix starting with a dot removed.
This worked fine for paths like /some/path/test-11.input. It also worked
for paths like /some/path/inline (there were no dots, so we got $f back unscathed).
But in the ubuntu CI the package is built in a temporary directory like
/tmp/autopkgtest-lxc.nnnfqb26/downtmp/build.UfW/ (yes, it has a dot, even two.).
That still worked for the first case, but in the second case we truncated things
after the first dot, and we would try to get
/tmp/autopkgtest-lxc.nnnfqb26/downtmp/build and try to load
/tmp/autopkgtest-lxc.nnnfqb26/downtmp/build.expected-password, which obviously
didn't work as expected. To avoid this issue, do the suffix removal only when
we know that there really is a suffix.

A second minor issue was that we would try to copy $1.expected-*, and sometimes
$1 would be given, and sometimes not. Effectively we were relying on there
not being any files matching .expected-*. There weren't any such files, but let's
avoid this ugliness and always pass $1.

test/test-sysusers.sh.in

@@ -27,12 +27,12 @@ preprocess() {
 }
 
 compare() {
-    if ! diff -u $TESTDIR/etc/passwd <(preprocess ${1%.*}.expected-passwd); then
-        echo "**** Unexpected output for $f"
+    if ! diff -u $TESTDIR/etc/passwd <(preprocess $1.expected-passwd); then
+        echo "**** Unexpected output for $f $2"
         exit 1
     fi
 
-    if ! diff -u $TESTDIR/etc/group <(preprocess ${1%.*}.expected-group); then
+    if ! diff -u $TESTDIR/etc/group <(preprocess $1.expected-group); then
         echo "**** Unexpected output for $f $2"
         exit 1
     fi
@@ -47,7 +47,7 @@ for f in $(ls -1 $SOURCE/test-*.input | sort -V); do
     cp $f $TESTDIR/usr/lib/sysusers.d/test.conf
     $SYSUSERS --root=$TESTDIR
 
-    compare $f ""
+    compare ${f%.*} ""
 done
 
 for f in $(ls -1 $SOURCE/test-*.input | sort -V); do
@@ -56,7 +56,7 @@ for f in $(ls -1 $SOURCE/test-*.input | sort -V); do
     touch $TESTDIR/etc/sysusers.d/test.conf
     cat $f | $SYSUSERS --root=$TESTDIR -
 
-    compare $f "on stdin"
+    compare ${f%.*} "on stdin"
 done
 
 for f in $(ls -1 $SOURCE/test-*.input | sort -V); do
@@ -68,12 +68,12 @@ for f in $(ls -1 $SOURCE/test-*.input | sort -V); do
     # this should be ignored
     cat $SOURCE/test-1.input | $SYSUSERS --root=$TESTDIR --replace=/usr/lib/sysusers.d/test.conf -
 
-    compare $f "on stdin with --replace"
+    compare ${f%.*} "on stdin with --replace"
 done
 
 # test --inline
 echo "*** Testing --inline"
-prepare_testdir
+prepare_testdir $SOURCE/inline
 # copy a random file to make sure it is ignored
 cp $f $TESTDIR/etc/sysusers.d/confuse.conf
 $SYSUSERS --root=$TESTDIR --inline \
@@ -84,7 +84,7 @@ compare $SOURCE/inline "(--inline)"
 
 # test --replace
 echo "*** Testing --inline with --replace"
-prepare_testdir
+prepare_testdir $SOURCE/inline
 # copy a random file to make sure it is ignored
 cp $f $TESTDIR/etc/sysusers.d/confuse.conf
 $SYSUSERS --root=$TESTDIR \