--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/bruterebase.py	Sun Aug 06 11:40:53 2017 -0700
@@ -0,0 +1,69 @@
+# bruterebase.py - brute force rebase testing
+#
+# Copyright 2017 Facebook, Inc.
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+from __future__ import absolute_import
+
+from mercurial import (
+    error,
+    registrar,
+    revsetlang,
+)
+
+from hgext import rebase
+
+cmdtable = {}
+command = registrar.command(cmdtable)
+
+@command('debugbruterebase')
+def debugbruterebase(ui, repo, source, dest):
+    """for every non-empty subset of source, run rebase -r subset -d dest
+
+    Print one line summary for each subset. Assume obsstore is enabled.
+    """
+    srevs = list(repo.revs(source))
+
+    with repo.wlock(), repo.lock():
+        repolen = len(repo)
+        cl = repo.changelog
+
+        def getdesc(rev):
+            result = cl.changelogrevision(rev).description
+            if rev >= repolen:
+                result += "'"
+            return result
+
+        for i in xrange(1, 2 ** len(srevs)):
+            subset = [rev for j, rev in enumerate(srevs) if i & (1 << j) != 0]
+            spec = revsetlang.formatspec('%ld', subset)
+            tr = repo.transaction('rebase')
+            tr.report = lambda x: 0 # hide "transaction abort"
+
+            ui.pushbuffer()
+            try:
+                rebase.rebase(ui, repo, dest=dest, rev=[spec])
+            except error.Abort as ex:
+                summary = 'ABORT: %s' % ex
+            except Exception as ex:
+                summary = 'CRASH: %s' % ex
+            else:
+                # short summary about new nodes
+                cl = repo.changelog
+                descs = []
+                for rev in xrange(repolen, len(repo)):
+                    desc = '%s:' % getdesc(rev)
+                    for prev in cl.parentrevs(rev):
+                        if prev > -1:
+                            desc += getdesc(prev)
+                    descs.append(desc)
+                descs.sort()
+                summary = ' '.join(descs)
+            ui.popbuffer()
+            repo.vfs.tryunlink('rebasestate')
+
+            subsetdesc = ''.join(getdesc(rev) for rev in subset)
+            ui.write(('%s: %s\n') % (subsetdesc.rjust(len(srevs)), summary))
+            tr.abort()

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/test-rebase-brute-force.t	Sun Aug 06 11:40:53 2017 -0700
@@ -0,0 +1,55 @@
+  $ cat >> $HGRCPATH <<EOF
+  > [extensions]
+  > drawdag=$TESTDIR/drawdag.py
+  > bruterebase=$TESTDIR/bruterebase.py
+  > [experimental]
+  > evolution=createmarkers,allowunstable
+  > EOF
+  $ init() {
+  >   N=`expr ${N:-0} + 1`
+  >   cd $TESTTMP && hg init repo$N && cd repo$N
+  >   hg debugdrawdag
+  > }
+
+Source looks like "N"
+
+  $ init <<'EOS'
+  > C D
+  > |\|
+  > A B Z
+  > EOS
+
+  $ hg debugbruterebase 'all()-Z' Z
+     A: A':Z
+     B: B':Z
+    AB: A':Z B':Z
+     C: ABORT: cannot use revision 3 as base, result would have 3 parents
+    AC: A':Z C':A'B
+    BC: B':Z C':B'A
+   ABC: A':Z B':Z C':A'B'
+     D: D':Z
+    AD: A':Z D':Z
+    BD: B':Z D':B'
+   ABD: A':Z B':Z D':B'
+    CD: CRASH: revlog index out of range
+   ACD: A':Z C':A'A' D':Z
+   BCD: B':Z C':B'A D':B'
+  ABCD: A':Z B':Z C':A'B' D':B'
+
+Moving backwards
+
+  $ init <<'EOS'
+  > C
+  > |\
+  > A B
+  > |
+  > Z
+  > EOS
+  $ hg debugbruterebase 'all()-Z' Z
+    B: B':Z
+    A: 
+   BA: B':Z
+    C: ABORT: cannot use revision 3 as base, result would have 3 parents
+   BC: B':Z C':B'A
+   AC: 
+  BAC: ABORT: nothing to merge