Wow, running under strace seems to seriously reduce the probability of whatever goes wrong, but it seems I finally got a run to fail under strace control:
sage -t /tmp/HOME/ttg.py
**********************************************************************
File "/tmp/HOME/ttg.py", line 36, in
ttg.ttFailed example:
S.betti()
Exception raised:
Traceback (most recent call last):
File "/usr/local/sage/sage-dev/local/lib/python2.7/site-packages/sage/doctest/forker.py", line 480, in _run
self.execute(example, compiled, test.globs)
File "/usr/local/sage/sage-dev/local/lib/python2.7/site-packages/sage/doctest/forker.py", line 839, in execute
exec compiled in globs
File "<doctest
ttg.tt[4]>", line 1, in <module>
S.betti()
File "/usr/local/sage/sage-dev/local/lib/python2.7/site-packages/sage/sandpiles/sandpile.py", line 2036, in betti
print singular.eval('print(betti(%s),"betti")'%self._
singular_resolution.name())
File "/usr/local/sage/sage-dev/local/lib/python2.7/site-packages/sage/sandpiles/sandpile.py", line 408, in __getattr__
self._set_resolution()
File "/usr/local/sage/sage-dev/local/lib/python2.7/site-packages/sage/sandpiles/sandpile.py", line 1909, in _set_resolution
row = new[j].transpose().sage_matrix(self._ring)
File "/usr/local/sage/sage-dev/local/lib/python2.7/site-packages/sage/interfaces/singular.py", line 1763, in sage_matrix
A[x,y]=R(self[x+1,y+1])
File "multi_polynomial_libsingular.pyx", line 807, in sage.rings.polynomial.multi_polynomial_libsingular.MPolynomialRing_libsingular.__call__ (sage/rings/polynomial/multi_polynomial_libsingular.cpp:6226)
File "/usr/local/sage/sage-dev/local/lib/python2.7/site-packages/sage/interfaces/singular.py", line 1245, in __repr__
elif self.type() == 'matrix':
File "/usr/local/sage/sage-dev/local/lib/python2.7/site-packages/sage/interfaces/singular.py", line 1976, in type
return m.group(1)
AttributeError: 'NoneType' object has no attribute 'group'