[PATCH 17/22] iotests: Add VM.assert_block_path()

[Max Reitz <mreitz@redhat.com>]

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 tests/qemu-iotests/iotests.py | 48 +++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/tests/qemu-iotests/iotests.py b/tests/qemu-iotests/iotests.py
index daed4ee013..e6fb46287d 100644
--- a/tests/qemu-iotests/iotests.py
+++ b/tests/qemu-iotests/iotests.py
@@ -670,6 +670,54 @@ class VM(qtest.QEMUQtestMachine):
 
         return fields.items() <= ret.items()
 
+    '''
+    @path is a string whose components are separated by slashes.
+    The first component is a node name, the rest are child names.
+    Examples:
+      - "qcow2-node/backing/file"
+      - "quorum-node/children.2/file"
+
+    @expected_node may be None.
+
+    @graph may be None or the result of an x-debug-query-block-graph
+    call that has already been performed.
+    '''
+    def assert_block_path(self, path, expected_node, graph=None):
+        if graph is None:
+            graph = self.qmp('x-debug-query-block-graph')['return']
+
+        iter_path = iter(path.split('/'))
+        root = next(iter_path)
+        try:
+            node = next(node for node in graph['nodes'] if node['name'] == root)
+        except StopIteration:
+            node = None
+
+        for path_node in iter_path:
+            assert node is not None, 'Cannot follow path %s' % path
+
+            try:
+                node_id = next(edge['child'] for edge in graph['edges'] \
+                                             if edge['parent'] == node['id'] and
+                                                edge['name'] == path_node)
+
+                node = next(node for node in graph['nodes'] \
+                                 if node['id'] == node_id)
+            except StopIteration:
+                node = None
+
+        assert node is not None or expected_node is None, \
+               'No node found under %s (but expected %s)' % \
+               (path, expected_node)
+
+        assert expected_node is not None or node is None, \
+               'Found node %s under %s (but expected none)' % \
+               (node['name'], path)
+
+        if node is not None and expected_node is not None:
+            assert node['name'] == expected_node, \
+                   'Found node %s under %s (but expected %s)' % \
+                   (node['name'], path, expected_node)
 
 index_re = re.compile(r'([^\[]+)\[([^\]]+)\]')
 
-- 
2.21.0