diff --git a/tests/testlib/badserverext.py b/tests/testlib/badserverext.py
--- a/tests/testlib/badserverext.py
+++ b/tests/testlib/badserverext.py
@@ -108,22 +108,25 @@
         orig = object.__getattribute__(obj, '_orig')
         bmethod = method.encode('ascii')
         func = getattr(orig, method)
-        # No byte limit on this operation. Call original function.
+
+        if remaining:
+            remaining = max(0, remaining)
+
         if not remaining:
-            result = func(data, *args, **kwargs)
-            obj._writelog(b'%s(%d) -> %s' % (bmethod, len(data), data))
-            return result
-
-        remaining = max(0, remaining)
-
-        if remaining > 0:
+            newdata = data
+        else:
             if remaining < len(data):
                 newdata = data[0:remaining]
             else:
                 newdata = data
+            remaining -= len(newdata)
+            self.remaining_send_bytes = remaining
 
-            remaining -= len(newdata)
+        result = func(newdata, *args, **kwargs)
 
+        if remaining is None:
+            obj._writelog(b'%s(%d) -> %s' % (bmethod, len(data), data))
+        else:
             obj._writelog(
                 b'%s(%d from %d) -> (%d) %s'
                 % (
@@ -135,11 +138,7 @@
                 )
             )
 
-            result = func(newdata, *args, **kwargs)
-
-        self.remaining_send_bytes = remaining
-
-        if remaining <= 0:
+        if remaining is not None and remaining <= 0:
             obj._writelog(b'write limit reached; closing socket')
             object.__getattribute__(obj, '_cond_close')()
             raise Exception('connection closed after sending N bytes')