regrtest: add -k and -K options to filter tests by function/file names

Lib/test/support.py

--- a/Lib/test/support.py
+++ b/Lib/test/support.py
@@ -1270,19 +1270,28 @@ def _run_suite(suite):
 
 def run_unittest(*classes):
     """Run tests from unittest.TestCase-derived classes."""
+    regexes = run_unittest.regexes
+    if regexes:
+        def filter_test(name):
+            return any(regex.search(name) for regex in regexes)
+    else:
+        filter_test = None
     valid_types = (unittest.TestSuite, unittest.TestCase)
     suite = unittest.TestSuite()
     for cls in classes:
         if isinstance(cls, str):
             if cls in sys.modules:
-                suite.addTest(unittest.findTestCases(sys.modules[cls]))
+                suite.addTest(unittest.findTestCases(sys.modules[cls], filter=filter_test))
             else:
                 raise ValueError("str arguments must be keys in sys.modules")
         elif isinstance(cls, valid_types):
             suite.addTest(cls)
         else:
-            suite.addTest(unittest.makeSuite(cls))
+            suite.addTest(unittest.makeSuite(cls, filter=filter_test))
     _run_suite(suite)
+# List of regex objects used to filter the tests by their function name.
+# An empty list means that all tests are used.
+run_unittest.regexes = []
 
 
 #=======================================================================