Is it possible to enable stderr in completion code?

When I run the test Y01completion.ztst
<https://github.com/paltherr/zsh/blob/fix-unset/Test/Y01completion.ztst>,
messages written to stderr within Zle/complete.c
<https://github.com/paltherr/zsh/blob/fix-unset/Src/Zle/complete.c> don't
show up anywhere. Thus, calls to DPUTS, like this one
<https://github.com/paltherr/zsh/blob/33d137b41886792563a09142519a1e555b249481/Src/Zle/complete.c#L1304>
will
never break any test even if they start triggering.

Is there a way to enable stderr, either with a change in Zsh code or in C
code?

I'm just looking for a way to test/debug a few changes in the Zle C code. I
would like that messages written to stderr in that code show up in the
output of tests like the one above. Any hack will do.

Philippe