diff4: is it actually used?

Hi devs,

In the context of the diff optimization patch I'm working on ([1]),
I'm wondering if diff4 is actually used in svn. If I look for usages
of subversion/libsvn_diff/diff4.c#svn_diff_diff4, I only come up with
tools/diff/diff4.c#main.

So: this code isn't used in the svn core itself? What's the use of the
diff4 executable in tools/diff? Is it for experimentation with that
implementation, but it never really got finalized to be taken up in
svn proper? Or am I overlooking something?

Also, tools/diff/diff4.c mentions the following description above the
copyright notice: "diff4-test.c -- test driver for 3-way text merges".
Wrong filename. And "test driver", what does that mean?

Background: I'm working on extending my patch to work for all diff's
in svn: normal diff, diff3 and diff4 (to avoid having to special case
things only for regular diff, and the patch is just as useful for
diffX as for regular diff). I don't want to break anything, so I was
looking around for ways how to exercise that code.

Should I take diff4 into account, and if so, how can I test it?

Cheers,

-- 
Johan
[1] http://svn.haxx.se/dev/archive-2010-10/0167.shtml