Why is netrc not supported? Is this just a temporary workaround to get the build passing all tests? Or it is something more fundamental?

If it is temporary, and likely to be fixed, then that intent should be documented near the skipif.

If it is permanent, then that reason should be documented both here and in the documentation for netrc. https://docs.python.org/3.10/library/netrc.html gives no hint that it might be missing in certain operating systems, let alone excluding VxWorks in particular.

And I suppose this comment applies globally to failures resolved by a skipIf, including those already integrated.

@JimJJewett Thanks for your review.
This is permanent design. VxWorks RTOS has no user home directory. So VxWorks native ftp client doesn't support auto-login feature. We also can't support this Python module. I've modified the docs as you requested.

And I suppose this comment applies globally to failures resolved by a skipIf, including those already integrated.

Yes. We have updated docs in the previous merged PRs and I will keep this in mind in the following PRs. Thanks.

I merged your PR, thanks. The final change is no longer specific to VxWorks and it makes the code cleaner, good!