Added test_afc.py

[afzal442]

Reference Issues/PRs

Fixes #483

What does this implement/fix? Explain your changes.

Added unit tests for the transformer

Does your contribution introduce a new dependency? If yes, which one?

No

PR checklist

• I've added myself to the list of contributors.
• Optionally, I've updated sktime's CODEOWNERS to receive notifications about future changes to these files.
• I've added unit tests and made sure they pass locally.
• I've added the transformers series to the file.
• I've updated the existing file.

[mloning]

@Afzal-Ind the unit tests looks great - exactly what I had in mind, good work! Could you add it to the other PR #509 so that it's all in one place?

[afzal442]

Could you add it to the other PR #509 so that it's all in one place?

Thanks a lot again for your guidance. I would add it definitely.

[mloning]

Closed in favour of #509