test: reproduce junction cleanup failure on Windows

test/blackbox-tests/setup-script.sh

@@ -121,3 +121,9 @@ build () {
 file_status() {
   [ -e "$1" ] && echo "$1 exists" || echo "$1 missing"
 }
+
+strip_sandbox() {
+  # we want to substitute it to $SANDBOX
+  # shellcheck disable=SC2016
+  dune_cmd subst '[^ ]*.sandbox[/\\][^/\\]+' '$SANDBOX'
+}

test/blackbox-tests/test-cases/cram/dune

@@ -16,3 +16,9 @@
 (cram
  (applies_to hg-access)
  (enabled_if %{bin-available:hg}))
+
+(cram
+ (applies_to junction-cleanup)
+ (enabled_if
+  (= %{os_type} Win32))
+ (alias runtest-windows))

test/blackbox-tests/test-cases/cram/junction-cleanup.t

@@ -0,0 +1,32 @@
+On Windows, MSYS2 may create junctions (directory reparse points) instead of
+proper symbolic links. OCaml's Unix.lstat returns ENOENT for junctions whose
+targets are unreachable, which causes them to be invisible to directory cleanup.
+
+This test verifies that the cram test runner can clean up after a test that
+creates junctions.
+
+This is currently not the case.
+
+  $ trap 'cmd /c "rmdir /s /q _build" 2>/dev/null' EXIT
+
+  $ cat > dune-project << EOF
+  > (lang dune 3.0)
+  > (cram enable)
+  > EOF
+
+Create a cram test that creates a junction inside its working directory:
+
+  $ cat > junction.t <<'EOF'
+  >   $ echo hi > file
+  >   $ cmd /c "mklink /j junction file" > /dev/null
+  > EOF
+
+  $ dune runtest 2>&1 | strip_sandbox
+  Error: failed to delete sandbox in
+  $SANDBOX
+  Reason:
+  $SANDBOX\default): Directory not empty
+  -> required by _build/default/.cram.junction.t/cram.out
+  -> required by alias junction
+  -> required by alias runtest
+  [1]

test/blackbox-tests/test-cases/pkg/helpers.sh

@@ -55,12 +55,6 @@ show_pkg() {
   find "$prefix" | sort | dune_cmd subst "$prefix" ""
 }
 
-strip_sandbox() {
-  # we want to substitute it to $SANDBOX
-  # shellcheck disable=SC2016
-  dune_cmd subst '[^ ]*.sandbox/[^/]+' '$SANDBOX'
-}
-
 show_pkg_targets() {
   local pkg=$1
   local prefix