Issue #12624: It is now possible to fail after the first failure when

running in verbose mode (`-v` or `-W`), by using the `--failfast`
(or `-G`) option to regrtest.  This is useful with long test suites
such as test_io or test_subprocess.

Lib/test/support.py

@@ -52,7 +52,7 @@ __all__ = [
     "reap_children", "cpython_only", "check_impl_detail", "get_attribute",
     "swap_item", "swap_attr", "requires_IEEE_754",
     "TestHandler", "Matcher", "can_symlink", "skip_unless_symlink",
-    "import_fresh_module"
+    "import_fresh_module", "failfast",
     ]
 
 class Error(Exception):
@@ -176,6 +176,7 @@ use_resources = None     # Flag set to [] by regrtest.py
 max_memuse = 0           # Disable bigmem tests (they will still be run with
                          # small sizes, to make sure they work.)
 real_max_memuse = 0
+failfast = False
 
 # _original_stdout is meant to hold stdout at the time regrtest began.
 # This may be "the real" stdout, or IDLE's emulation of stdout, or whatever.
@@ -1186,7 +1187,8 @@ def check_impl_detail(**guards):
 def _run_suite(suite):
     """Run tests from a unittest.TestSuite-derived class."""
     if verbose:
-        runner = unittest.TextTestRunner(sys.stdout, verbosity=2)
+        runner = unittest.TextTestRunner(sys.stdout, verbosity=2,
+                                         failfast=failfast)
     else:
         runner = BasicTestRunner()