test: "detect" the test number automagically

Specifying the test number manually is tedious and prone to errors (as
recently proven). Since we have all the necessary data to work out the
test number, let's do it automagically.

test/test-functions

@@ -57,7 +57,7 @@ fi
 
 # The calling test.sh scripts have TEST_BASE_DIR set via their Makefile, but we don't need them to provide it
 TEST_BASE_DIR=${TEST_BASE_DIR:-$(realpath "$(dirname "${BASH_SOURCE[0]}")")}
-TEST_UNITS_DIR="$TEST_BASE_DIR/units"
+TEST_UNITS_DIR="$(realpath "$TEST_BASE_DIR/units")"
 SOURCE_DIR=$(realpath "$TEST_BASE_DIR/..")
 TOOLS_DIR="$SOURCE_DIR/tools"
 # These variables are used by test scripts
@@ -91,6 +91,17 @@ STATEFILE="$STATEDIR/.testdir"
 IMAGESTATEDIR="$STATEDIR/.."
 TESTLOG="$STATEDIR/test.log"
 
+if ! [[ "$TESTNAME" =~ ^TEST\-([0-9]+)\-.+$ ]]; then
+    echo "ERROR: Test name '$TESTNAME' is not in the expected format: TEST-[0-9]+-*" >&2
+    exit 1
+fi
+TESTID="${BASH_REMATCH[1]:?}"
+
+if [[ ! -f "$TEST_UNITS_DIR/testsuite-$TESTID.service" ]]; then
+    echo "ERROR: Test '$TESTNAME' is missing its service file '$TEST_UNITS_DIR/testsuite-$TESTID.service" >&2
+    exit 1
+fi
+
 BASICTOOLS=(
     awk
     basename
@@ -2444,7 +2455,7 @@ do_test() {
         case $1 in
             --run)
                 echo "${testname} RUN: $TEST_DESCRIPTION"
-                test_run "$2"
+                test_run "$TESTID"
                 ret=$?
                 if [ $ret -eq 0 ]; then
                     echo "${testname} RUN: $TEST_DESCRIPTION [OK]"
@@ -2475,7 +2486,7 @@ do_test() {
                     test_setup_cleanup </dev/null >>"$TESTLOG" 2>&1 || ret=$?
                 fi
                 if [ $ret -eq 0 ]; then
-                    test_run "$2" </dev/null >>"$TESTLOG" 2>&1 || ret=$?
+                    test_run "$TESTID" </dev/null >>"$TESTLOG" 2>&1 || ret=$?
                 fi
                 test_cleanup
                 if [ $ret -eq 0 ]; then