Add env variable GRPC_DNS_RESOLVER
diff --git a/tools/run_tests/run_tests.py b/tools/run_tests/run_tests.py
index 05f819b..d1b8733 100755
--- a/tools/run_tests/run_tests.py
+++ b/tools/run_tests/run_tests.py
@@ -230,6 +230,9 @@
                  _ROOT + '/src/core/lib/tsi/test_creds/ca.pem',
              'GRPC_POLL_STRATEGY': polling_strategy,
              'GRPC_VERBOSITY': 'DEBUG'}
+        resolver = os.environ.get('GRPC_DNS_RESOLVER', None);
+        if resolver:
+          env['GRPC_DNS_RESOLVER'] = resolver
         shortname_ext = '' if polling_strategy=='all' else ' GRPC_POLL_STRATEGY=%s' % polling_strategy
         if self.config.build_config in target['exclude_configs']:
           continue