ch 19, eunit: Why use ?cmd("rm filename") instead of file:delete("filename")

[Steven Wicklund]

In chapter 19 the eunit tests use the ?cmd() macro instead of
file:delete/1. Why is this? I was getting a test exception using
this syntax(enoent) that went away when I switched to delete.
Some weirdness here: ?cmd is described as being OS dependent - I run
on Win7 so I tried using the "del" command to no avail, but now I
notice that several other tests use the ?cmd("rm ...") notation
successfully. Is ?cmd in fact OS specific, or will it translate a "rm
filename" to "del filename" on Windows?

[Steven Wicklund]

I figured out what that I was writing my test cases improperly and
that the ?cmd("rm...") fails every time.