add try/except to import StringIO for test_print function

Author: ishiland

tests/unit/test_help.py

@@ -1,8 +1,8 @@
-import io
 import sys
 
 from ..testcase import TestCase
 
+
 class TestHelp(TestCase):
 
     def test_get_function_list(self):
@@ -26,7 +26,14 @@ def test_invalid_function_help(self):
         self.assertEqual(h, "Function 'fake' does not exist.")
 
     def test_print(self):
-        h = io.StringIO()
+
+        try:
+            import StringIO  # python 2
+            h = StringIO.StringIO()
+        except ImportError:
+            import io  # python 3
+            h = io.StringIO()
+
         sys.stdout = h
 
         o = self.geosupport.help()