apache/spark — pull request #2759 by cocoatomo (2014-10-11 03:08:25+00:00)
Title: [SPARK-3867] ./python/run-tests failed when it run with Python 2.6 and unittest2 is not installed

./python/run-tests search a Python 2.6 executable on PATH and use it if available.
When using Python 2.6, it is going to import unittest2 module which is not a standard library in Python 2.6, so it fails with ImportError.