Fix decoders tests

[luabida]

=========================== short test summary info ============================
FAILED pysus/tests/test_decoders.py::TestDecoder::test_group_and_count - Attr...
FAILED pysus/tests/test_decoders.py::TestDecoder::test_redistribute - Attribu...
FAILED pysus/tests/test_decoders.py::TestDecoder::test_translate_variables - ...
FAILED pysus/tests/test_sim.py::TestDecoder::test_group_and_count - Attribute...
FAILED pysus/tests/test_sim.py::TestDecoder::test_redistribute_missing - Attr...
FAILED pysus/tests/test_sim.py::TestDecoder::test_redistribute_missing_partial
== 6 failed, 53 passed, 8 skipped, 1 xfailed, 7 warnings in 668.75s (0:11:08) ==