Fixes issue #444 in test_lump, test_hasbits and test_graph

I reduced the memory requirements for test_lump.py, test_hasbits.py and test_graph.py.

- [ ] Is it mergable
- [ ] Did it pass the tests?
- [ ] If it introduces new functionality in scripts/ is it tested?
  Check for code coverage.
- [ ] Is it well formatted? Look at `pep8`/`pylint`, `cppcheck`, and
  `make doc` output. Use `autopep8` and `astyle -A10 --max-code-length=80`
  if needed.
- [ ] Is it documented in the Changelog?
- [ ] Was spellcheck run on the source code and documentation after changes
  were made?