rr_graph: Start trying to rebuild an existing rr_graph

Signed-off-by: John McMaster <johndmcmaster@gmail.com>
Signed-off-by: Tim 'mithro' Ansell <me@mith.ro>

v2x/lib/asserts.py

diff --git a/v2x/lib/asserts.py b/v2x/lib/asserts.py
index 775f00b..fdbf2db 100644
--- a/v2x/lib/asserts.py
+++ b/v2x/lib/asserts.py
@@ -18,9 +18,9 @@
     )
 
 
-def assert_eq(a, b):
+def assert_eq(a, b, msg=None):
     """Assert equal with better error message."""
-    assert a == b, __safe_error("!=", a, b)
+    assert a == b, msg or __safe_error("!=", a, b)
 
 
 def assert_is(a, b):