Issue #25795: Fix several tests to run independently.
These were broken in 3aec776fc796 when they were converted
away from using support.run_unittest(). Oops :)
Initial patch by Felippe da Motta Raposo.
diff --git a/Lib/test/test_wait4.py b/Lib/test/test_wait4.py
index 43869be..3e6a79d 100644
--- a/Lib/test/test_wait4.py
+++ b/Lib/test/test_wait4.py
@@ -4,6 +4,7 @@
import os
import time
import sys
+import unittest
from test.fork_wait import ForkWait
from test.support import reap_children, get_attribute