Most test files use a testing infrastructure from t/test_utils.pl.  In that
case the references for the test of a test category $test_category.t file 
are in  t/results/$test_category/.  They are regenerated with the -g option 
given to the .t file, as in

  perl -w t/60macro.t -g

To regenerate a precise test reference file, the test name should be in
argument, for example to regenerate the reference files for 
arg_body_expansion_order:

  perl -w t/60macro.t -g arg_body_expansion_order


From the top directory, you can also create texinfo files corresponding with
tests by running something along

  perl -w t/60macro.t -c

to create a file for each of the test in t/60macro.t, or for a specific
test, here arg_body_expansion_order: 

  perl -w t/60macro.t -c arg_body_expansion_order


The output files will be created with -o, in t/output_files/$test_category/