Isn't the change in io.registry._get_valid_format already being tested in test_read_toomanyformats? That is running the code to raise an exception and validating the output.

@mwcraig - overall this looks good, thanks! We should wait to see if @astrofrog wants to have a look before merging.

@taldcroft -- thanks for the feedback! What test_read_toomanyformats doesn't test is the case when the sorted in io.registry._get_valid_format resorts to comparing the objects because the names are the same.

I don't think it needs a separate test necessarily, since the same fix is tested in test_register_readers_with_same_name_on_different_classes...but it was a code change without a corresponding test so I wanted to point it out.

@mwcraig - I agree that the code looks fine and doesn't need a separate test.

Looks good - thanks @mwcraig!