[Exim] Condition line in a director

I'm trying to write a director (exim 3) that will activate on recieving
a certain subject line. Unfortunately I can't get it to work. My main
problem is I can't figure out if it's because $h_subject isn't available
or if I'm doing the condition wrong. If I put a line like the following
in the director:

condition = "${if def:header_subject:{yes}{no}}"

the test passes and the director is taken.

However if I then try to actually test on the subject header with the
following

condition = "${if eq{$header_subject:}{test}{yes}{no}}"


I could probably do what I need to do in a global filter file but I'm
curious if I've misunderstood how condition works or if the header just
isn't available where I need it.

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