tests: add basic test for sys install

tests/setup_disk_test

@@ -11,6 +11,7 @@ init_tests \
 	setup_disk_func_find_efi_size \
 	setup_disk_func_uuid_or_device \
 	setup_disk_non_existing_block_dev \
+	setup_disk_sys \
 	setup_disk_install_mounted_root_nvme \
 	setup_disk_install_mounted_root_efi \
 	setup_disk_install_mounted_root_efi_boot \
@@ -45,6 +46,7 @@ fake_disk() {
 
 	echo $(( $size * 1000000 / $blocksize )) > sys/block/$dev/size
 	echo $(( $blocksize )) > sys/block/$dev/queue/logical_block_size
+	truncate -s "${size}M" dev/"$dev"
 }
 
 
@@ -251,6 +253,15 @@ setup_disk_non_existing_block_dev_body() {
 		setup-disk -m sys /dev/vda
 }
 
+setup_disk_sys_body() {
+	init_env
+	fake_disk vda
+	mkdir proc etc
+	touch proc/mounts etc/fstab
+	ERASE_DISKS=/dev/vda atf_check \
+		setup-disk -m sys /dev/vda
+}
+
 setup_disk_install_mounted_root_nvme_body() {
 	init_env
 	mkdir -p target/boot/efi \