--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/test-dirstate-version-fallback.t	Sun Jun 18 00:09:39 2023 +0200
@@ -0,0 +1,51 @@
+  $ cat >> $HGRCPATH << EOF
+  > [storage]
+  > dirstate-v2.slow-path=allow
+  > [format]
+  > use-dirstate-v2=no
+  > EOF
+
+Set up a v1 repo
+
+  $ hg init repo
+  $ cd repo
+  $ echo a > a
+  $ hg add a
+  $ hg commit -m a
+  $ hg debugrequires | grep dirstate
+  [1]
+  $ ls -1 .hg/dirstate*
+  .hg/dirstate
+
+Copy v1 dirstate
+  $ cp .hg/dirstate $TESTTMP/dirstate-v1-backup
+
+Upgrade it to v2
+
+  $ hg debugupgraderepo -q --config format.use-dirstate-v2=1 --run | egrep 'added:|removed:'
+     added: dirstate-v2
+  $ hg debugrequires | grep dirstate
+  dirstate-v2
+  $ ls -1 .hg/dirstate*
+  .hg/dirstate
+  .hg/dirstate.* (glob)
+
+Manually reset to dirstate v1 to simulate an incomplete dirstate-v2 upgrade
+
+  $ rm .hg/dirstate*
+  $ cp $TESTTMP/dirstate-v1-backup .hg/dirstate
+
+There should be no errors, but a v2 dirstate should be written back to disk
+  $ hg st
+  $ ls -1 .hg/dirstate*
+  .hg/dirstate
+  .hg/dirstate.* (glob)
+
+Corrupt the dirstate to see how the errors show up to the user
+  $ echo "I ate your data" > .hg/dirstate
+
+  $ hg st
+  abort: working directory state appears damaged! (no-rhg !)
+  (falling back to dirstate-v1 from v2 also failed) (no-rhg !)
+  abort: Too little data for dirstate: 16 bytes. (rhg !)
+  [255]