zts: allow running a single test by name only

Specifying a single test is kind of a hassle, because the full relative
path under the test suite dir has to be included, but it's not always
clear what that path even is.

This change allows `-t` to take the name of a single test instead of a
full path. If the value has no `/` characters, we search for a file of
that name under the test root, and if found, use that as the full test
path instead.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Akash B <akash-b@hpe.com>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #16088

scripts/zfs-tests.sh

@@ -326,7 +326,8 @@ OPTIONS:
 	-d DIR      Use world-writable DIR for files and loopback devices
 	-s SIZE     Use vdevs of SIZE (default: 4G)
 	-r RUNFILES Run tests in RUNFILES (default: ${DEFAULT_RUNFILES})
-	-t PATH     Run single test at PATH relative to test suite
+	-t PATH|NAME  Run single test at PATH relative to test suite,
+	                or search for test by NAME
 	-T TAGS     Comma separated list of tags (default: 'functional')
 	-u USER     Run single test as USER (default: root)
 
@@ -340,6 +341,9 @@ $0 -r linux-fast
 # Run a single test
 $0 -t tests/functional/cli_root/zfs_bookmark/zfs_bookmark_cliargs.ksh
 
+# Run a single test by name
+$0 -t zfs_bookmark_cliargs
+
 # Cleanup a previous run of the test suite prior to testing, run the
 # default ($(echo "${DEFAULT_RUNFILES}" | sed 's/\.run//')) suite of tests and perform no cleanup on exit.
 $0 -x
@@ -450,8 +454,15 @@ post_user = root
 post =
 outputdir = /var/tmp/test_results
 EOF
-	SINGLETESTDIR="${SINGLETEST%/*}"
+	if [ "$SINGLETEST" = "${SINGLETEST%/*}" ] ; then
+		NEWSINGLETEST=$(find "$STF_SUITE" -name "$SINGLETEST*" -print -quit)
+		if [ -z "$NEWSINGLETEST" ] ; then
+			fail "couldn't find test matching '$SINGLETEST'"
+		fi
+		SINGLETEST=$NEWSINGLETEST
+	fi
 
+	SINGLETESTDIR="${SINGLETEST%/*}"
 	SETUPDIR="$SINGLETESTDIR"
 	[ "${SETUPDIR#/}" = "$SETUPDIR" ] && SETUPDIR="$STF_SUITE/$SINGLETESTDIR"
 	[ -x "$SETUPDIR/setup.ksh"   ] && SETUPSCRIPT="setup"     || SETUPSCRIPT=