Test that comment is reread

Tests/test_file_jpeg.py

@@ -86,18 +86,26 @@ def test_app(self):
             assert len(im.applist) == 2
 
             assert im.info["comment"] == b"File written by Adobe Photoshop\xa8 4.0\x00"
+            assert im.app["COM"] == im.info["comment"]
 
-    def test_com_write(self):
-        dummy_text = "this is a test comment"
+    def test_comment_write(self):
         with Image.open(TEST_FILE) as im:
-            with BytesIO() as buf:
-                im.save(buf, format="JPEG")
-                with Image.open(buf) as im2:
-                    assert im.app["COM"] == im2.app["COM"]
-            with BytesIO() as buf:
-                im.save(buf, format="JPEG", comment=dummy_text)
-                with Image.open(buf) as im2:
-                    assert im2.app["COM"].decode() == dummy_text
+            assert im.info["comment"] == b"File written by Adobe Photoshop\xa8 4.0\x00"
+
+            # Test that existing comment is saved by default
+            out = BytesIO()
+            im.save(out, format="JPEG")
+            with Image.open(out) as reloaded:
+                assert im.info["comment"] == reloaded.info["comment"]
+
+            # Test that a comment argument overrides the default comment
+            for comment in ("Test comment text", b"Text comment text"):
+                out = BytesIO()
+                im.save(out, format="JPEG", comment=comment)
+                with Image.open(out) as reloaded:
+                    if not isinstance(comment, bytes):
+                        comment = comment.encode()
+                    assert reloaded.info["comment"] == comment
 
     def test_cmyk(self):
         # Test CMYK handling.  Thanks to Tim and Charlie for test data,