diff --git a/syncplay/localtesting.py b/syncplay/localtesting.py
new file mode 100644
index 0000000..316dcd2
--- /dev/null
+++ b/syncplay/localtesting.py
@@ -0,0 +1,56 @@
+#coding:utf8
+'''
+Monkey patches for testing with emulated network latency and time offset
+'''
+
+from collections import deque
+import os
+import time
+import random
+
+from twisted.internet import reactor
+
+from . import network_utils
+
+
+try:
+    OFFSET = float(os.environ['OFFSET'])
+except (ValueError, KeyError):
+    pass
+else:
+    orig_time = time.time
+    def new_time(*args, **kwargs):
+        return orig_time(*args, **kwargs) + OFFSET
+    time.time = new_time
+
+try:
+    LAG_MU = float(os.environ['LAG_MU'])
+    LAG_SIGMA = float(os.environ['LAG_SIGMA'])
+except (ValueError, KeyError):
+    pass
+else:
+    random.seed()
+    OriginalCommandProtocol = network_utils.CommandProtocol
+
+    class LaggedCommandProtocol(OriginalCommandProtocol):
+        def __init__(self, *args, **kwargs):
+            self._queue_in = deque()
+            self._queue_out = deque()
+            OriginalCommandProtocol.__init__(self, *args, **kwargs)
+
+        def lineReceived(self, line):
+            self._queue_in.append(line)
+            reactor.callLater(
+                abs(random.gauss(LAG_MU, LAG_SIGMA)),
+                lambda: OriginalCommandProtocol.lineReceived(self, self._queue_in.popleft())
+            )
+
+        def sendLine(self, line):
+            self._queue_out.append(line)
+            reactor.callLater(
+                abs(random.gauss(LAG_MU, LAG_SIGMA)),
+                lambda: OriginalCommandProtocol.sendLine(self, self._queue_out.popleft())
+            )
+
+    network_utils.CommandProtocol = LaggedCommandProtocol
+