This outputs
#+RESULTS:
| (linenum:0, |
| 4 |
I suppose the issue is the "linenum:0". In fact, running any of the test src blocks does that, e.g.
#+begin_src maxima :results verbatim :batch batch
(assume(z>0),
integrate(exp(-t)*t^z, t, 0, inf));
#+end_src
#+RESULTS:
#+begin_example
(linenum:0,
(assume(z > 0),integrate(exp(-t)*t^z,t,0,inf))
gamma(z + 1)
#+end_example
This does not match the (should (equal ...)) in test-ob-maxima.el
I don't know maxima, and haven't made any explicit modifications regards it, so I don't know why my setup would be outputting linenum:0