[SPARK-3867] ./python/run-tests failed when it run with Python 2.6 and unittest2 is not installed

Author: cocoatomo

python/pyspark/mllib/tests.py

@@ -25,7 +25,11 @@
 from numpy import array, array_equal
 
 if sys.version_info[:2] <= (2, 6):
-    import unittest2 as unittest
+    try:
+        import unittest2 as unittest
+    except ImportError:
+        sys.stderr.write('Please install unittest2 to test with Python 2.6 or earlier')
+        sys.exit(1)
 else:
     import unittest
 

python/pyspark/tests.py

@@ -34,7 +34,11 @@
 from platform import python_implementation
 
 if sys.version_info[:2] <= (2, 6):
-    import unittest2 as unittest
+    try:
+        import unittest2 as unittest
+    except ImportError:
+        sys.stderr.write('Please install unittest2 to test with Python 2.6 or earlier')
+        sys.exit(1)
 else:
     import unittest