diff --git a/src/wormhole_transit_relay/test/common.py b/src/wormhole_transit_relay/test/common.py
index fb232b5..8073ee0 100644
--- a/src/wormhole_transit_relay/test/common.py
+++ b/src/wormhole_transit_relay/test/common.py
@@ -55,8 +55,11 @@ class ServerBase:
         self._setup_relay(blur_usage=blur_usage)
 
     def flush(self):
+        did_work = False
         for pump in self._pumps:
-            pump.flush()
+            did_work = pump.flush() or did_work
+        if did_work:
+            self.flush()
 
     def _setup_relay(self, blur_usage=None, log_file=None, usage_db=None):
         self._transit_server = Transit(
diff --git a/src/wormhole_transit_relay/test/test_transit_server.py b/src/wormhole_transit_relay/test/test_transit_server.py
index e44b099..8fbdef8 100644
--- a/src/wormhole_transit_relay/test/test_transit_server.py
+++ b/src/wormhole_transit_relay/test/test_transit_server.py
@@ -61,7 +61,6 @@ class _Transit:
         self.flush()
         p2.send(handshake(token1, side=None))
         self.flush()
-        self.flush()
 
         # a correct handshake yields an ack, after which we can send
         exp = b"ok\n"
@@ -89,7 +88,6 @@ class _Transit:
         self.flush()
         p2.send(handshake(token1, side=None))
         self.flush()
-        self.flush()
 
         # a correct handshake yields an ack, after which we can send
         exp = b"ok\n"
@@ -117,7 +115,6 @@ class _Transit:
         p1.send(handshake(token1, side=None))
         p2.send(handshake(token1, side=side1))
         self.flush()
-        self.flush()
 
         # a correct handshake yields an ack, after which we can send
         exp = b"ok\n"
@@ -147,7 +144,6 @@ class _Transit:
         self.flush()
         p2.send(handshake(token1, side=side2))
         self.flush()
-        self.flush()
 
         # a correct handshake yields an ack, after which we can send
         exp = b"ok\n"
@@ -187,7 +183,6 @@ class _Transit:
         side2 = b"\x02"*8
         p3.send(handshake(token1, side=side2))
         self.flush()
-        self.flush()
         self.assertEqual(self.count(), 0)
         self.assertEqual(len(self._transit_server._pending_requests), 0)
         self.assertEqual(len(self._transit_server._active_connections), 2)
@@ -453,7 +448,6 @@ class Usage(ServerBase, unittest.TestCase):
 
         p2.send(handshake(token1, side=side2))
         self.flush()
-        self.flush()
         self.assertEqual(len(self._transit_server._pending_requests), 0)
         self.assertEqual(len(self._usage), 2, self._usage)
         (started, result, total_bytes, total_time, waiting_time) = self._usage[1]