diff --git a/tests/.gitignore b/tests/.gitignore
index 32ad161c..18878dab 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -12,3 +12,4 @@ src/o_tmpfile_umask
 src/o_tmpfile_linkat
 src/mmap_stress
 src/mmap_validate
+src/totl-delta-inject
diff --git a/tests/Makefile b/tests/Makefile
index 3a2380dc..dd6b8409 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -15,7 +15,8 @@ BIN := src/createmany			\
 	src/o_tmpfile_umask		\
 	src/o_tmpfile_linkat		\
 	src/mmap_stress			\
-	src/mmap_validate
+	src/mmap_validate		\
+	src/totl-delta-inject
 
 DEPS := $(wildcard src/*.d)
 
diff --git a/tests/golden/totl-delta-inject b/tests/golden/totl-delta-inject
new file mode 100644
index 00000000..c98f1976
--- /dev/null
+++ b/tests/golden/totl-delta-inject
@@ -0,0 +1,10 @@
+== setup three files contributing to totl 8888.0.0
+== merge baseline into fs_root
+8888.0.0 = 42, 3
+== inject (+128, +2) unbalances totl 8888.0.0
+8888.0.0 = 170, 5
+== unlink f3 (value 32) produces a -32/-1 delta
+8888.0.0 = 138, 4
+== inject (-128, -2) restores accounting for the remaining files
+8888.0.0 = 10, 2
+== cleanup
diff --git a/tests/sequence b/tests/sequence
index 3107975d..d2ac6a0d 100644
--- a/tests/sequence
+++ b/tests/sequence
@@ -29,6 +29,7 @@ totl-xattr-tag.sh
 basic-xattr-indx.sh
 quota.sh
 totl-merge-read.sh
+totl-delta-inject.sh
 lock-refleak.sh
 lock-shrink-consistency.sh
 lock-shrink-read-race.sh
diff --git a/tests/src/totl-delta-inject.c b/tests/src/totl-delta-inject.c
new file mode 100644
index 00000000..10f7f68c
--- /dev/null
+++ b/tests/src/totl-delta-inject.c
@@ -0,0 +1,121 @@
+/*
+ * Test helper that calls SCOUTFS_IOC_INJECT_TOTL_DELTA to seed
+ * arbitrary totl deltas.
+ *
+ * Copyright (C) 2026 Versity Software, Inc.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ */
+
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <inttypes.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <sys/ioctl.h>
+#include <linux/types.h>
+
+#include "ioctl.h"
+
+static void usage(const char *prog)
+{
+	fprintf(stderr,
+		"Usage: %s <mountpoint> <a>.<b>.<c> <total> <count>\n",
+		prog);
+	exit(2);
+}
+
+static int parse_s64(const char *s, int64_t *out)
+{
+	char *end;
+	int64_t v;
+
+	errno = 0;
+	v = strtoll(s, &end, 0);
+	if (errno || *end != '\0' || end == s)
+		return -1;
+	*out = v;
+	return 0;
+}
+
+/*
+ * Parse "<a>.<b>.<c>" into abc[0..2] (skxt_a, skxt_b, skxt_c).  Each
+ * component must be a non-empty unsigned base-0 integer.
+ */
+static int parse_dotted_name(const char *s, uint64_t abc[3])
+{
+	const char *p = s;
+	char *end;
+	int i;
+
+	for (i = 0; i < 3; i++) {
+		if (*p == '\0' || *p == '.')
+			return -1;
+		errno = 0;
+		abc[i] = strtoull(p, &end, 0);
+		if (errno || end == p)
+			return -1;
+
+		if (i < 2) {
+			if (*end != '.')
+				return -1;
+			p = end + 1;
+		} else {
+			if (*end != '\0')
+				return -1;
+		}
+	}
+	return 0;
+}
+
+int main(int argc, char **argv)
+{
+	struct scoutfs_ioctl_inject_totl_delta itd = { 0 };
+	uint64_t abc[3];
+	int64_t total, count;
+	int fd;
+	int ret;
+
+	if (argc != 5)
+		usage(argv[0]);
+
+	if (parse_dotted_name(argv[2], abc) ||
+	    parse_s64(argv[3], &total) ||
+	    parse_s64(argv[4], &count)) {
+		fprintf(stderr, "could not parse arguments\n");
+		usage(argv[0]);
+	}
+
+	itd.name[0] = abc[0];
+	itd.name[1] = abc[1];
+	itd.name[2] = abc[2];
+	itd.total = total;
+	itd.count = count;
+
+	fd = open(argv[1], O_RDONLY | O_DIRECTORY);
+	if (fd < 0) {
+		fprintf(stderr, "open(%s): %s\n", argv[1], strerror(errno));
+		return 1;
+	}
+
+	ret = ioctl(fd, SCOUTFS_IOC_INJECT_TOTL_DELTA, &itd);
+	if (ret < 0) {
+		fprintf(stderr,
+			"INJECT_TOTL_DELTA(%" PRIu64 ".%" PRIu64 ".%" PRIu64
+			", total=%" PRId64 ", count=%" PRId64 "): %s\n",
+			abc[0], abc[1], abc[2], total, count, strerror(errno));
+		close(fd);
+		return 1;
+	}
+
+	close(fd);
+	return 0;
+}
diff --git a/tests/tests/totl-delta-inject.sh b/tests/tests/totl-delta-inject.sh
new file mode 100644
index 00000000..772ec365
--- /dev/null
+++ b/tests/tests/totl-delta-inject.sh
@@ -0,0 +1,43 @@
+#
+# Exercise the SCOUTFS_IOC_INJECT_TOTL_DELTA ioctl that injects totl
+# deltas directly via totl-delta-inject(1).
+#
+
+t_require_commands setfattr scoutfs sync rm touch totl-delta-inject
+
+# force a log merge then read-xattr-totals filtered to our own keys
+read_totals()
+{
+	t_force_log_merge
+	sync
+	echo 1 > $(t_debugfs_path)/drop_weak_item_cache
+	scoutfs read-xattr-totals -p "$T_M0" | \
+		grep -E '^8888\.' || true
+}
+
+echo "== setup three files contributing to totl 8888.0.0"
+touch "$T_D0/f1" "$T_D0/f2" "$T_D0/f3"
+setfattr -n scoutfs.totl.inj.8888.0.0 -v 2  "$T_D0/f1"
+setfattr -n scoutfs.totl.inj.8888.0.0 -v 8  "$T_D0/f2"
+setfattr -n scoutfs.totl.inj.8888.0.0 -v 32 "$T_D0/f3"
+
+echo "== merge baseline into fs_root"
+read_totals
+
+echo "== inject (+128, +2) unbalances totl 8888.0.0"
+totl-delta-inject "$T_M0" 8888.0.0 128 2
+read_totals
+
+echo "== unlink f3 (value 32) produces a -32/-1 delta"
+rm -f "$T_D0/f3"
+read_totals
+
+echo "== inject (-128, -2) restores accounting for the remaining files"
+totl-delta-inject "$T_M0" 8888.0.0 -128 -2
+read_totals
+
+echo "== cleanup"
+rm -f "$T_D0/f1" "$T_D0/f2"
+read_totals
+
+t_pass