Fix run_tests script for Mac
diff --git a/tools/run_tests/run_tests.py b/tools/run_tests/run_tests.py
index 196e26e..1a16b09 100755
--- a/tools/run_tests/run_tests.py
+++ b/tools/run_tests/run_tests.py
@@ -75,8 +75,9 @@
 
 
 _POLLING_STRATEGIES = {
-  'linux': ['epollsig', 'poll', 'poll-cv']
+  'linux': ['epollsig', 'poll', 'poll-cv'],
 # TODO(ctiller, sreecha): enable epoll1, epollex, epoll-thread-pool
+  'mac': ['poll'],
 }