Dynamic modules: should should-error work?

[Eli Zaretskii]

It looks like should-error doesn't work with functions implemented in
modules.  For example, try this in modules/mod-test/test.el:

  (ert-deftest mod-test-sum-test ()
    (should-error (mod-test-sum 1 2 3)))

I cannot get this test to succeed, although the error message about
wrong number of arguments is emitted.  What am I missing?