[Exim] Multi-condition ACL statement in a macro possible?

I'm trying to define a macro holding a short multi-condition ACL
statement in Exim 4.22; but I can't seem to get it to do the
linebreaks properly. If it is possible at all, what would be
the syntax to put the following ACL into a macro? (If I can
get this simple case to work, it should be possible to extrapolate
to more complex statements.)

    warn    message = X-Test: YES
        condition = ${if {$h_subject}{macro test}{yes}{no}}

No matter what combination of \ and \n I try, it seems to always
make the condition part of the X-Test header's value. Or an "unknown
ACL condition/modifier" error message.



Thanks,
-Pat