It's straightforward to set up GDB to quickly invoke pg_hexedit on a page image, without going through the filesystem. The page image can even come from a local temp buffer.
A user-defined GDB command can be created that shows an arbitrary page image in pg_hexedit from an interactive GDB session.
This is a good way to understand what's really going on when debugging access method code. It also works well with core dumps. I found this valuable during a recent project to improve the Postgres B-Tree code.
An example of how to make this work is available from a newly added section of the pg_hexedit README file: