Backwards compatible means it's a drop-in replacement.
> How can you be sure that something is "backwards compatible"?
You compare the outputs from the same inputs.
> the original coreutils did not have a test for this particular edge case
So? 'man date' shows this argument option. Just because there was no existing unit test for it doesn't mean it's ok to break it. It would have taken literally 10 seconds to compare the outputs from the old and new program.
Backwards compatible means it's a drop-in replacement.
> How can you be sure that something is "backwards compatible"?
You compare the outputs from the same inputs.
> the original coreutils did not have a test for this particular edge case
So? 'man date' shows this argument option. Just because there was no existing unit test for it doesn't mean it's ok to break it. It would have taken literally 10 seconds to compare the outputs from the old and new program.