def is_string(obj):
        return isinstance(obj, basestring)
test that create a supplement issue, with ``volume``, ``suppl_text`` and empty ``number`` fields.
dataset/ETHPy150Open python-openxml/python-docx/docx/opc/compat.py/is_string--crossover with--dataset/ETHPy150Open scieloorg/scielo-manager/scielomanager/api/tests_resources_v2.py/IssuesRestAPITest.test_suppl_volume_filter_without_number