original from https://github.com/4paradigm/OpenMLDB/issues/339
Please send PR to our GitHub repo https://github.com/4paradigm/OpenMLDB

The unit test of TestWindowUnion is ignored because of https://github.com/4paradigm/OpenMLDB/issues/122 .

Once the bug has been fixed, we should enable this unit test to ensure the functionality.

It is a low-hanging fruit and we just need to uncomment the code in TestWindowUnion.scala to enable the unit test.