[3.6] bpo-29512, bpo-30776: Backport regrtest enhancements from master to 3.6 (#2513)

* bpo-29512: Add test.bisect, bisect failing tests (#2452)

Add a new "python3 -m test.bisect" tool to bisect failing tests.

It can be used to find which test method(s) leak references, leak
files, etc.
(cherry picked from commit 84d9d14a1fa395fbd21262ba195490be25a7b3bc)

* bpo-30776: regrtest: reduce memleak false positive (#2484)

Only report a leak if each run leaks at least one memory block.
(cherry picked from commit beeca6e1e5fd01531b1db7059498b13d07dca525)

1 files changed, 3 insertions, 10 deletions

diff --git a/Lib/test/libregrtest/refleak.py b/Lib/test/libregrtest/refleak.py
index 8e18d75..8e93816 100644
--- a/Lib/test/libregrtest/refleak.py
+++ b/Lib/test/libregrtest/refleak.py
@@ -96,6 +96,8 @@ def dash_R(the_module, test, indirect_test, huntrleaks):
 
     # These checkers return False on success, True on failure
     def check_rc_deltas(deltas):
+        # Checker for reference counters and memomry blocks.
+        #
         # bpo-30776: Try to ignore false positives:
         #
         #   [3, 0, 0]
@@ -108,22 +110,13 @@ def dash_R(the_module, test, indirect_test, huntrleaks):
         #   [10, 1, 1]
         return all(delta >= 1 for delta in deltas)
 
-    def check_alloc_deltas(deltas):
-        # At least 1/3rd of 0s
-        if 3 * deltas.count(0) < len(deltas):
-            return True
-        # Nothing else than 1s, 0s and -1s
-        if not set(deltas) <= {1,0,-1}:
-            return True
-        return False
-
     def check_fd_deltas(deltas):
         return any(deltas)
 
     failed = False
     for deltas, item_name, checker in [
         (rc_deltas, 'references', check_rc_deltas),
-        (alloc_deltas, 'memory blocks', check_alloc_deltas),
+        (alloc_deltas, 'memory blocks', check_rc_deltas),
         (fd_deltas, 'file descriptors', check_fd_deltas)
     ]:
         # ignore warmup runs