tests/int: add a case for cgroupv2 mount

This checks that in-container view of /sys/fs/cgroup does not
contain any extra cgroups (which was the case for rootless
before the previous commit).

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

tests/integration/cgroups.bats

@@ -281,3 +281,18 @@ function setup() {
 
 	check_cpu_weight 42
 }
+
+@test "runc run (cgroupv2 mount inside container)" {
+	requires cgroups_v2
+	[[ "$ROOTLESS" -ne 0 ]] && requires rootless_cgroup
+
+	set_cgroups_path
+
+	runc run -d --console-socket "$CONSOLE_SOCKET" test_cgroups_unified
+	[ "$status" -eq 0 ]
+
+	# Make sure we don't have any extra cgroups inside
+	runc exec test_cgroups_unified find /sys/fs/cgroup/ -type d
+	[ "$status" -eq 0 ]
+	[ "$(wc -l <<<"$output")" -eq 1 ]
+}