Move test_gdbm to use unittest.

Closes issue #1960. Thanks Giampaolo Rodola.
diff --git a/Misc/NEWS b/Misc/NEWS
index 7743e0b..764b68e 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -50,6 +50,8 @@
 Tests
 -----
 
+- Issue 1960: Convert test_gdbm to unittest.
+
 - GHOP 294: Convert test_contains, test_crypt, and test_select to unittest.
 
 - GHOP 238: Convert test_tokenize to use doctest.