On macOS windows are not allowed to overlap the menubar at the top of the screen.
If you ask the Apple window manager to position a window with y-coordinate 0 it
will instead position it with y-coordinate equal to 23, the height of the
menubar.

There are a number of unixWm tests which use the wm geometry command to position
a window with y-coordinate < 23 and then check, using the wm geometry command,
that it actually was placed at the requested position.  These cannot pass on
macOS.

In my first round of making the unixWm tests pass on the mac I added code which
would essentially lie to Tk in this situation.  When a position was requested
that would cause a window to overlap the menubar, the position recorded in the
wmInfo struct was the requested position, not the actual position where the Apple
window manager drew the window.

This was not a good idea.  It would be better to record the actual window
position and adjust the tests for Aqua so they are not expecting impossible
results.