Style fix

Author: gaborgsomogyi

python/pyspark/sql/tests/test_streaming.py

@@ -237,7 +237,7 @@ def _assert_exception_tree_contains_msg(self, exception, msg):
         while e.cause is not None and not contains:
             e = e.cause
             contains = msg in e.desc
-        self.assertTrue(contains, "Exception tree doesn't contain the expected message: %s" %msg)
+        self.assertTrue(contains, "Exception tree doesn't contain the expected message: %s" % msg)
 
     def test_query_manager_await_termination(self):
         df = self.spark.readStream.format('text').load('python/test_support/sql/streaming')