LogDog: Properly emit Butler stream magic.

client/libs/logdog/tests/stream_test.py

Index: client/libs/logdog/tests/stream_test.py
diff --git a/client/libs/logdog/tests/stream_test.py b/client/libs/logdog/tests/stream_test.py
index c05d05f08f8804b751e32c6f13d73a18cdfd7bca..98cbbdacb971f7362546eb45df12b4afdefe2f44 100755
--- a/client/libs/logdog/tests/stream_test.py
+++ b/client/libs/logdog/tests/stream_test.py
@@ -84,6 +84,10 @@ class StreamClientTestCase(unittest.TestCase):
 
     def interpret(self):
       data = StringIO.StringIO(self.buffer.getvalue())
+      magic = data.read(len(stream.BUTLER_MAGIC))
+      if magic != stream.BUTLER_MAGIC:
+        raise ValueError('Invalid magic value ([%s] != [%s])' % (
+            magic, stream.BUTLER_MAGIC))
       length, _ = varint.read_uvarint(data)
       header = data.read(length)
       return json.loads(header), data.read()