diff --git a/parso/python/diff.py b/parso/python/diff.py
index 2255b5c..5be6acb 100644
--- a/parso/python/diff.py
+++ b/parso/python/diff.py
@@ -17,6 +17,25 @@ from parso.python.tokenize import PythonToken
 from parso.python.token import PythonTokenTypes
 
 LOG = logging.getLogger(__name__)
+DEBUG_DIFF_PARSER = False
+
+
+def _assert_valid_graph(node):
+    """
+    Checks if the parent/children relationship is correct.
+    """
+    try:
+        children = node.children
+    except AttributeError:
+        previous_leaf = node.get_previous_leaf()
+        if previous_leaf is not None:
+            assert previous_leaf.end_pos <= node.start_pos, \
+                (previous_leaf, node)
+        return
+
+    for child in children:
+        assert child.parent == node
+        _assert_valid_graph(child)
 
 
 def _get_last_line(node_or_leaf):
@@ -171,7 +190,12 @@ class DiffParser(object):
                 % (last_pos, line_length, parso.__version__, ''.join(diff))
             )
 
-        #assert self._module.get_code() == ''.join(new_lines)
+        if DEBUG_DIFF_PARSER:
+            # If there is reasonable suspicion that the diff parser is not
+            # behaving well, this should be enabled.
+            assert self._module.get_code() == ''.join(new_lines)
+            _assert_valid_graph(self._module)
+
         LOG.debug('diff parser end')
         return self._module
 
diff --git a/test/test_diff_parser.py b/test/test_diff_parser.py
index eaf748c..8df6402 100644
--- a/test/test_diff_parser.py
+++ b/test/test_diff_parser.py
@@ -6,7 +6,7 @@ import pytest
 from parso.utils import split_lines
 from parso import cache
 from parso import load_grammar
-from parso.python.diff import DiffParser
+from parso.python.diff import DiffParser, _assert_valid_graph
 from parso import parse
 
 
@@ -34,24 +34,6 @@ def _check_error_leaves_nodes(node):
     return False
 
 
-def _assert_valid_graph(node):
-    """
-    Checks if the parent/children relationship is correct.
-    """
-    try:
-        children = node.children
-    except AttributeError:
-        previous_leaf = node.get_previous_leaf()
-        if previous_leaf is not None:
-            assert previous_leaf.end_pos <= node.start_pos, \
-                (previous_leaf, node)
-        return
-
-    for child in children:
-        assert child.parent == node
-        _assert_valid_graph(child)
-
-
 class Differ(object):
     grammar = load_grammar()