btrfs-progs: misc-test: Add regression test for find-root gives empty result

Add regression test for btrfs-find-root gives empty result even the fs
is OK.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
[ enhanced test ]
Signed-off-by: David Sterba <dsterba@suse.com>

tests/misc-tests/012-find-root-no-result/test.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+# Regression test for case btrfs-find-root may print no result on a
+# recent fs or balanced fs, whose metadata chunk is the first chunk
+# and the only metadata chunk
+
+source $TOP/tests/common
+
+check_prereq btrfs-find-root
+check_prereq btrfs-image
+
+run_check $TOP/btrfs-image -r first_meta_chunk.btrfs-image test.img || \
+	_fail "failed to extract first_meta_chunk.btrfs-image"
+
+result=$(run_check_stdout $TOP/btrfs-find-root test.img | sed '/^Superblock/d')
+
+if [ -z "$result" ]; then
+	_fail "btrfs-find-root failed to find tree root"
+fi
+
+if ! echo "$result" | grep -q 'Found tree root at'; then
+	_fail "btrfs-find-root failed to find tree root, unexpected output"
+fi
+
+rm test.img