The python test on travis now takes twice as long as it was a few days ago.
In this case serveral days ago it only takes about 15 minutes, more detail can be found in 
But now it takes about half an hour, more detail can be found in 
It seems that a lot of time is spent on the newly added test cases in `test_udf.py`. We need some optimization for these test cases to reduce test time.
What do you think?