diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index 809c662124..8c6d327b03 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -1996,6 +1996,41 @@ test_trace2_data () {
 	grep -e '"category":"'"$1"'","key":"'"$2"'","value":"'"$3"'"'
 }
 
+# Check that the given trace2 data event has the expected value and
+# appears exactly once.  Produces a diagnostic on failure.
+#
+#	test_trace2_data_singular <category> <key> <value> [<label>]
+test_trace2_data_singular () {
+	local category="$1" key="$2" expect_val="$3"
+	local label_suffix="${4:+ [$4]}"
+	local kv_pattern='"category":"'"$category"'","key":"'"$key"'","value":"\([^"]*\)"'
+	local actual
+
+	actual=$(sed -n "s|.*${kv_pattern}.*|\1|p") &&
+
+	if test -z "$actual"
+	then
+		echo >&4 "error: trace2 data '$category/$key'$label_suffix not found"
+		return 1
+	fi &&
+
+	case "$actual" in
+	*"$LF"*)
+		echo >&4 "error: trace2 data '$category/$key'$label_suffix has multiple entries, expected 1"
+		printf '%s\n' "$actual" | sed 's/^/  actual:   /' >&4
+		return 1
+		;;
+	esac &&
+
+	if test "$actual" != "$expect_val"
+	then
+		echo >&4 "error: trace2 data '$category/$key'$label_suffix"
+		echo >&4 "  expected: $expect_val"
+		echo >&4 "  actual:   $actual"
+		return 1
+	fi
+}
+
 # Given a GIT_TRACE2_EVENT log over stdin, writes to stdout a list of URLs
 # sent to git-remote-https child processes.
 test_remote_https_urls() {