SymPy testsuite marks some tests as "slow"?

The SymPy Gruntz testsuite<https://github.com/sympy/sympy/blob/master/sympy/series/tests/test_gruntz.py> appears to have a mechanism for skipping slow tests (see lines 33 and 98, for example). There are other such designations as well, for example:

  *
test_grunts_eval_special_slow_sometimes_fail (line 137 — “grunts” looks like a typo)
  *
test_gruntz_eval_special_fail (line 148)
  *
test_gruntz_eval_special (line 110)

What does “sometimes_fail” mean? Every third Tuesday?
I’m not sure we want to complicate our own tests by optionally skipping tests and so on, but perhaps I lack imagination?
I noticed this because I was working on some known testsuite failures. My “improved” code increases the running time for:
(%i1) limit(exp(exp(exp(psi[0](psi[0](psi[0](x))))))/x, x, inf);
(%o1)                                  0

(%i2) time(%);
(%o2)                             [14.640625]

from about 0.01 seconds to close to 15 seconds. I’m suspicious that current Maxima gets the correct value for this limit by “magic,” not logic. Tracing a few functions shows that this test almost behaves like an infinite loop — I suspect a near‑bug in my code.
In SymPy, this test (line 133) is marked as slow. How slow is it in SymPy?
--Barton

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