avocado..tree: Overwrite multiplex only when explicitely asked for

Originally we used multiplex = True and False. This patch adds None and
the value is not updated during merge when the new node's multiplex is
None.

Currently this means that once node is set as multiplex, there is no way
to undo this. We might consider creating !nomux flag in the future to
force multiplex = False, but this is currently not needed.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

avocado/core/tree.py

@@ -89,7 +89,7 @@ class TreeNode(object):
         self._environment = None
         self.environment_origin = {}
         self.ctrl = []
-        self.multiplex = False
+        self.multiplex = None
         for child in children:
             self.add_child(child)
 
@@ -159,7 +159,10 @@ class TreeNode(object):
                             remove.append(key)
                     for key in remove:
                         self.value.pop(key, None)
-        self.multiplex = other.multiplex
+        if other.multiplex is True:
+            self.multiplex = True
+        elif other.multiplex is False:
+            self.multiplex = False
         self.value.update(other.value)
         for child in other.children:
             self.add_child(child)

selftests/all/unit/avocado/tree_unittest.py

@@ -171,20 +171,20 @@ class TestTree(unittest.TestCase):
         self.assertEqual({'new_value': 'something'},
                          oldroot.children[3].children[0].children[0].value)
         # multiplex root (always True)
-        self.assertEqual(tree2.multiplex, False)
+        self.assertEqual(tree2.multiplex, None)
         # multiplex /virt/
-        self.assertEqual(tree2.children[0].multiplex, False)
+        self.assertEqual(tree2.children[0].multiplex, None)
         # multiplex /virt/hw
-        self.assertEqual(tree2.children[0].children[0].multiplex, False)
+        self.assertEqual(tree2.children[0].children[0].multiplex, None)
         # multiplex /virt/distro
         self.assertEqual(tree2.children[0].children[1].multiplex, True)
         # multiplex /virt/env
         self.assertEqual(tree2.children[0].children[2].multiplex, True)
         # multiplex /virt/absolutly
-        self.assertEqual(tree2.children[0].children[3].multiplex, False)
+        self.assertEqual(tree2.children[0].children[3].multiplex, None)
         # multiplex /virt/distro/fedora
         self.assertEqual(tree2.children[0].children[1].children[0].multiplex,
-                         False)
+                         None)
 
 
 class TestPathParent(unittest.TestCase):