Add test for -save-as {slice} (#3801, #3802)

Original report: https://community.aseprite.org/t/17692

tests/cli/save-as.sh

@@ -314,3 +314,11 @@ $ASEPRITE -b sprites/1empty3.aseprite \
 expect "a1.png
 a2.png
 b.png" "list_files $d"
+
+# Regression with -save-as {slice}
+# https://github.com/aseprite/aseprite/issues/3801
+
+d=$t/save-as-with-slice
+$ASEPRITE -b sprites/slices.aseprite -save-as $d/{slice}.png
+expect "square.png
+line.png" "list_files $d"

tests/sprites/README.md

@@ -26,4 +26,5 @@
 * `2f-index-3x3.aseprite`: Indexed, 2 frames, 1 layer, mask color set
   to index 21.
 * `file-tests-props.aseprite`: Indexed, 64x64, 6 frames, 4 layers (one
-   of them is a tilemap), 13 cels, 1 tag.
+   of them is a tilemap), 13 cels, 1 tag.
+* `slices.aseprite`: Indexed, 4x4, background layer, 2 slices.