Strange "make check" error

[David Kastrup]

My issue 4357 patchy borked at me again.  However, the log file shows
invoking gs -sDEVICE=png16m -dGraphicsAlphaBits=4 -dTextAlphaBits=4  
-slilypond-datadir=input/regression/out-test/share/lilypond/current   -r101  
-sOutputFile=/tmp/build-lilypond-autobuild/out/test-results/input/regression/out-test/test-output-distance.png
 -dNOSAFER -dEPSCrop -q -dNOPAUSE  
input/regression/out-test/test-output-distance.eps  -c quit 
pipe file 
/tmp/build-lilypond-autobuild/out/test-results/input/regression/out-test-baseline/test-output-distance.png
pipe file 
/tmp/build-lilypond-autobuild/out/test-results/input/regression/out-test/test-output-distance.png
dir is /tmp/tmp3QnpUl
invoking convert -depth 8 -crop 355x107+0+0 
/tmp/build-lilypond-autobuild/out/test-results/input/regression/out-test-baseline/test-output-distance.png
 /tmp/tmp3QnpUl/crop1.png
invoking convert -depth 8 -crop 355x107+0+0 
/tmp/build-lilypond-autobuild/out/test-results/input/regression/out-test/test-output-distance.png
 /tmp/tmp3QnpUl/crop2.png
invoking compare -depth 8 -dissimilarity-threshold 1 /tmp/tmp3QnpUl/crop1.png 
/tmp/tmp3QnpUl/crop2.png /tmp/tmp3QnpUl/diff.png
Traceback (most recent call last):
  File "/tmp/build-lilypond-autobuild/scripts/build/out/output-distance", line 
1342, in <module>
    main ()
  File "/tmp/build-lilypond-autobuild/scripts/build/out/output-distance", line 
1339, in main
    compare_tree_pairs (zip (args[0::2], args[1::2]), out, options.threshold)
  File "/tmp/build-lilypond-autobuild/scripts/build/out/output-distance", line 
1060, in compare_tree_pairs
    data.create_html_result_page (dest_dir, threshold)
  File "/tmp/build-lilypond-autobuild/scripts/build/out/output-distance", line 
1042, in create_html_result_page
    link.link_files_for_html (dest_dir)
  File "/tmp/build-lilypond-autobuild/scripts/build/out/output-distance", line 
674, in link_files_for_html
    compare_png_images (old, new, dest_dir)
  File "/tmp/build-lilypond-autobuild/scripts/build/out/output-distance", line 
92, in compare_png_images
    system ('compare -depth 8 -dissimilarity-threshold 1 %(dir)s/crop1.png 
%(dir)s/crop2.png %(dir)s/diff.png' % locals ())
  File "/tmp/build-lilypond-autobuild/scripts/build/out/output-distance", line 
1090, in system
    assert stat == 0
AssertionError
rm -rf /tmp/tmp3QnpUl
/tmp/lilypond-autobuild/GNUmakefile.in:325: recipe for target 'local-check' 
failed
make: *** [local-check] Error 1

Never seen anything like that.  I suppose it will be a fluke and
rerunning the test will "fix" it, but has anybody encountered anything
like that?  Strange bugout in the middle of the image comparisons?

-- 
David Kastrup