diff --git a/lib/common/tests/strings/Makefile.am b/lib/common/tests/strings/Makefile.am
index 6f3e100d5e..73e373a69d 100644
--- a/lib/common/tests/strings/Makefile.am
+++ b/lib/common/tests/strings/Makefile.am
@@ -1,40 +1,41 @@
 #
 # Copyright 2020-2022 the Pacemaker project contributors
 #
 # The version control history for this file may have further details.
 #
 # This source code is licensed under the GNU General Public License version 2
 # or later (GPLv2+) WITHOUT ANY WARRANTY.
 #
 
 AM_CPPFLAGS = -I$(top_srcdir)/include -I$(top_builddir)/include
 LDADD = $(top_builddir)/lib/common/libcrmcommon.la -lcmocka
 
 include $(top_srcdir)/mk/tap.mk
 
 # Add "_test" to the end of all test program names to simplify .gitignore.
 check_PROGRAMS = \
 		crm_get_msec_test 	\
 		crm_is_true_test 	\
 		crm_str_to_boolean_test 	\
 		pcmk__add_word_test		\
 		pcmk__btoa_test			\
 		pcmk__char_in_any_str_test	\
 		pcmk__compress_test	\
 		pcmk__ends_with_test 		\
 		pcmk__guint_from_hash_test	\
 		pcmk__numeric_strcasecmp_test \
 		pcmk__parse_ll_range_test	\
 		pcmk__scan_double_test		\
 		pcmk__scan_min_int_test		\
 		pcmk__scan_port_test		\
 		pcmk__starts_with_test 		\
 		pcmk__str_any_of_test		\
 		pcmk__str_in_list_test		\
 		pcmk__str_table_dup_test	\
+		pcmk__str_update_test		\
 		pcmk__strcmp_test 			\
 		pcmk__strkey_table_test 	\
 		pcmk__strikey_table_test 	\
 		pcmk__trim_test
 
 TESTS = $(check_PROGRAMS)
diff --git a/lib/common/tests/strings/pcmk__str_update_test.c b/lib/common/tests/strings/pcmk__str_update_test.c
new file mode 100644
index 0000000000..3f5cb30ade
--- /dev/null
+++ b/lib/common/tests/strings/pcmk__str_update_test.c
@@ -0,0 +1,69 @@
+/*
+ * Copyright 2022 the Pacemaker project contributors
+ *
+ * The version control history for this file may have further details.
+ *
+ * This source code is licensed under the GNU Lesser General Public License
+ * version 2.1 or later (LGPLv2.1+) WITHOUT ANY WARRANTY.
+ */
+
+#include <crm_internal.h>
+
+#include <stdarg.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <setjmp.h>
+#include <cmocka.h>
+
+static void
+update_null(void **state) {
+    char *str = NULL;
+
+    // These just make sure they don't crash
+    pcmk__str_update(NULL, NULL);
+    pcmk__str_update(NULL, "value");
+
+    // Update an already NULL string to NULL
+    pcmk__str_update(&str, NULL);
+    assert_null(str);
+
+    // Update an already allocated string to NULL
+    str = strdup("hello");
+    pcmk__str_update(&str, NULL);
+    assert_null(str);
+}
+
+static void
+update_same(void **state) {
+    char *str = NULL;
+    char *saved = NULL;
+
+    str = strdup("hello");
+    saved = str;
+    pcmk__str_update(&str, "hello");
+    assert_ptr_equal(saved, str); // No free and reallocation
+    free(str);
+}
+
+static void
+update_different(void **state) {
+    char *str = NULL;
+
+    str = strdup("hello");
+    pcmk__str_update(&str, "world");
+    assert_string_equal(str, "world");
+    free(str);
+}
+
+int
+main(int argc, char **argv)
+{
+    const struct CMUnitTest tests[] = {
+        cmocka_unit_test(update_null),
+        cmocka_unit_test(update_same),
+        cmocka_unit_test(update_different),
+    };
+
+    cmocka_set_message_output(CM_OUTPUT_TAP);
+    return cmocka_run_group_tests(tests, NULL, NULL);
+}