Improve tests for Becker & Hickl functions

[tritemio]

As mentioned in #46, it would be nice to improve tests for the functions for loading Becker&Hikl files. The tests are in test_bhreader.py.

This can be a relatively easy task for a new contributor and would make reading BH files more robust in the long term.

PR adding one or more tests are very welcome and will be merged.

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Technical description:
Right now there is a single test in nose format. It would be nice to convert this test to the simpler pytest format for consistency with test_pqreader.py (which can be used as an example).

Also, a simple smoke test for bh_print_sys_params() (and other functions) would be useful to avoid future breakage.