From e44f5677805affe4cda896e143c14f945a52c87a Mon Sep 17 00:00:00 2001
From: Glenn Maynard <glenn@zewt.org>
Date: Tue, 23 Oct 2018 22:34:29 -0500
Subject: [PATCH] Add a test for an image that works with other GIF decoders.

This test is fixed by the next commits.
---
 Tests/images/transparent_dispose.gif | Bin 0 -> 95 bytes
 Tests/test_file_gif.py               |  20 ++++++++++++++++++++
 2 files changed, 20 insertions(+)
 create mode 100644 Tests/images/transparent_dispose.gif

diff --git a/Tests/images/transparent_dispose.gif b/Tests/images/transparent_dispose.gif
new file mode 100644
index 0000000000000000000000000000000000000000..92b615543de7a4c82a3a3449e27b81d8efa7d4fe
GIT binary patch
literal 95
zcmZ?wbhEHbWM*Jwn8?7u@LvLmfiw^({$ye0Vqjv>0dYX`3`|TRAs}H+BQ)Wb0I+JX
PFi;&(Em*Y=BZD;nY>Eoh

literal 0
HcmV?d00001

diff --git a/Tests/test_file_gif.py b/Tests/test_file_gif.py
index 6a4b14d40..f1d9d688f 100644
--- a/Tests/test_file_gif.py
+++ b/Tests/test_file_gif.py
@@ -273,6 +273,26 @@ class TestFileGif(PillowTestCase):
         except EOFError:
             pass
 
+    def test_n_frames_invariant(self):
+        # Regression test: make sure that reading n_frames doesn't cause the
+        # current image to change.
+        img = Image.open("Tests/images/transparent_dispose.gif")
+        before = img.tobytes()
+
+        self.assertEqual(img.n_frames, 3)
+        self.assertEqual(before, img.tobytes())
+
+    def test_transparent_dispose(self):
+        img = Image.open("Tests/images/transparent_dispose.gif")
+
+        expected_colors = [(2, 1, 2), (0, 1, 0), (2, 1, 2)]
+        for frame in range(3):
+            img.seek(frame)
+            for x in range(3):
+                color = img.getpixel((x,0))
+                self.assertEqual(color, expected_colors[frame][x],
+                    'frame %i, x %i' % (frame, x))
+
     def test_dispose_previous(self):
         img = Image.open("Tests/images/dispose_prev.gif")
         try: