1 files changed, 2 insertions, 0 deletions
diff --git a/tests/server.py b/tests/server.py
index 984cfe26d4..7919a1f124 100644
--- a/tests/server.py
+++ b/tests/server.py
@@ -57,6 +57,8 @@ class FakeChannel(object):
         self.result["headers"] = headers
 
     def write(self, content):
+        assert isinstance(content, bytes), "Should be bytes! " + repr(content)
+
         if "body" not in self.result:
             self.result["body"] = b""