[Beginner Question]Is there way to test the postgres's kernel function?

Hi community,

I am learning the kernel of the postgres, and I want to test the make_relative_path function to know what it's operational principle.(I can read it's code, and I want to actually run it)

But I really don't know how to do it, wrtite a extension?

Can someone give me some advice?

Thanks in advance!

Yours,

Wen Yi.