.asc files are registered with the test system (by the ASCII output thorn) as output files to be compared and must be columnar ASCII data files. However periodic_weight enables output for grid_coordinates.asc which do not adhere to that format and instead contain descriptions of the boxes:

# grid coordinates
# format: map reflevel region mglevel   bounding-box
iteration 0
maps 1
0 mglevels 1
0 0 reflevels 1
0 0 0 regions 1
0 0 0 0   ([-2.6,-2.6,-2.6]:[2.4,2.4,2.4]:[0.2,0.2,0.2]/[0,0,0]:[0,0,0]/[26,26,26]/17576)

which causes the test system to complain:

Argument "([-2.6,-2.6,-2.6]:[2.4,2.4,2.4]:[0.2,0.2,0.2]/[0,0,0]:[0..." isn't numeric in subtraction (-) at lib/sbin/RunTestUtils.pl line 1920, <INNEW> line 8.

the testsuite should be changed to not output this file or give a different name that does not match one of the registered extensions.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2667/test-periodic_weight-of-carpetreduce