Add tests to compare different sprites (Sprite vs Layer mainly)

Related to: https://github.com/aseprite/aseprite/issues/3218

LICENSE.txt

@@ -1,4 +1,4 @@
-Copyright (c) 2018-2021 Igara Studio S.A.
+Copyright (c) 2018-2022 Igara Studio S.A.
 Copyright (c) 2018 David Capello
 
 Permission is hereby granted, free of charge, to any person obtaining

scripts/color.lua

@@ -1,3 +1,4 @@
+-- Copyright (C) 2022  Igara Studio S.A.
 -- Copyright (C) 2018  David Capello
 --
 -- This file is released under the terms of the MIT license.
@@ -41,3 +42,4 @@ assert(b.saturation == 0.4)
 assert(b.value == 0.5)
 assert(b.alpha == 200)
 assert(a == b)
+assert(a ~= 1) -- Comparing with other type fails

scripts/layers.lua

@@ -1,4 +1,4 @@
--- Copyright (C) 2019  Igara Studio S.A.
+-- Copyright (C) 2019-2022  Igara Studio S.A.
 -- Copyright (C) 2018  David Capello
 --
 -- This file is released under the terms of the MIT license.
@@ -204,3 +204,12 @@ do
     i = i + 1
   end
 end
+
+-- Compare layers vs sprites (just return false)
+
+do
+  local s = Sprite(2, 2)
+  assert(s.layers[1].parent == s)
+  assert(s.layers[1] ~= s) -- Uses Layer_eq() to compare
+  assert(s ~= s.layers[1]) -- Uses Sprite_eq() to compare
+end

scripts/sprite.lua

@@ -1,4 +1,4 @@
--- Copyright (C) 2019-2021  Igara Studio S.A.
+-- Copyright (C) 2019-2022  Igara Studio S.A.
 -- Copyright (C) 2018  David Capello
 --
 -- This file is released under the terms of the MIT license.
@@ -197,3 +197,12 @@ do
   assert(s.cels[1].image:getPixel(0, 0) == 2)
   assert(s.cels[1].image:getPixel(1, 0) == 1) -- Get the color of the first layer
 end
+
+-- Compare sprite IDs
+
+do
+  local a = Sprite(1, 1)
+  local b = Sprite(1, 1)
+  assert(a == a)
+  assert(a ~= b) -- Compares IDs, not sprite size
+end