Updated channel_dict regression test for IM7 support

tests/image_test.py

@@ -1128,6 +1128,8 @@ def test_metadata(fx_asset):
         assert img.metadata.get('exif:UnknownValue', "IDK") == "IDK"
 
 
+@mark.xfail(MAGICK_VERSION_NUMBER >= 0x700,
+            reason="Channel traits are not implemented in IM7.")
 def test_channel_depths(fx_asset):
     with Image(filename=str(fx_asset.join('beach.jpg'))) as i:
         assert dict(i.channel_depths) == {
@@ -1151,10 +1153,22 @@ def test_channel_depths(fx_asset):
 def test_channel_images(fx_asset):
     with Image(filename=str(fx_asset.join('sasha.jpg'))) as i:
         i.format = 'png'
-        for name in 'opacity', 'alpha', 'true_alpha':
+        channels = ('opacity', 'alpha',)
+        # Only include TrueAlphaChannel if IM6, as its deprecated & unused
+        # in IM7.
+        if MAGICK_VERSION_NUMBER < 0x700:
+            channels = channels + ('true_alpha',)
+        for name in channels:
             expected_path = str(fx_asset.join('channel_images', name + '.png'))
             with Image(filename=expected_path) as expected:
-                assert i.channel_images[name] == expected
+                if MAGICK_VERSION_NUMBER >= 0x700:
+                    # With IM7, channels are dynamic & influence signatures.
+                    # We'll need to compare the first channel of the expected
+                    # PNG with the extracted channel.
+                    first_channel = expected.channel_images['red']
+                    assert i.channel_images[name] == first_channel
+                else:
+                    assert i.channel_images[name] == expected
 
 
 def test_composite(fx_asset):