1 files changed, 51 insertions, 0 deletions
diff --git a/internal/engine/undo_identity_test.go b/internal/engine/undo_identity_test.go
index 9c93b3b..d4169be 100644
--- a/internal/engine/undo_identity_test.go
+++ b/internal/engine/undo_identity_test.go
@@ -223,3 +223,54 @@ func TestUndoLeavesNoDirectoriesBehind(t *testing.T) {
 		t.Errorf("dl/Out is left behind: %v", err)
 	}
 }
+
+// TestUndoCanBeFinishedAfterAFailure: an undo whose last reversal failed
+// (something took the original name) leaves the file part way back; once
+// the obstacle is gone, undoing the same run again offers only the step
+// that is left, and finishes it (review M10).
+func TestUndoCanBeFinishedAfterAFailure(t *testing.T) {
+	e, run, h, logPath := appliedRun(t, map[string]map[string]string{"dl": {"a.pdf": "one"}},
+		map[string]string{"dl": "(path \"~/dl\")\n(rule \"r\" (rename \"r-{name}\") (move \"Out\"))\n"})
+	up, err := e.PlanUndo(run)
+	if err != nil {
+		t.Fatal(err)
+	}
+	blocker := filepath.Join(h, "dl", "a.pdf")
+	if err := os.WriteFile(blocker, []byte("in the way"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	undo := func(up *UndoPlan) *ApplyResult {
+		t.Helper()
+		j, err := journal.Open(logPath)
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer j.Close()
+		res, err := e.ApplyUndo(context.Background(), up, j, journal.NewRunID(time.Now()))
+		if err != nil {
+			t.Fatal(err)
+		}
+		return res
+	}
+	if res := undo(up); res.Failed != 1 {
+		t.Fatalf("first undo: Failed = %d, want 1 (the rename back is blocked)", res.Failed)
+	}
+	if err := os.Remove(blocker); err != nil {
+		t.Fatal(err)
+	}
+	time.Sleep(10 * time.Millisecond) // a new run id
+	again, err := e.PlanUndo(run)
+	if err != nil {
+		t.Fatal(err)
+	}
+	f := undoFileNamed(t, again, "dl", "a.pdf")
+	if f.Refused != "" || len(f.Steps) != 1 || f.Steps[0].Action != "undo-rename" {
+		t.Fatalf("second plan: %+v; want one undo-rename step", f)
+	}
+	if res := undo(again); res.Failed != 0 || res.Applied != 1 {
+		t.Fatalf("second undo: %+v", res)
+	}
+	if b, err := os.ReadFile(filepath.Join(h, "dl", "a.pdf")); err != nil || string(b) != "one" {
+		t.Errorf("dl/a.pdf = %q, %v; want the original back", b, err)
+	}
+}