How to use the docxcompose.properties.ComplexField function in docxcompose

def test_identifies_complex_fields_correctly(self):
        document = Document(docx_path('three_props_in_same_paragraph.docx'))
        properties = CustomProperties(document).find_docprops_in_document()

        assert 1 == len(document.paragraphs), 'input file should contains one paragraph'
        assert 3 == len(properties), \
            'input should contain three complex field docproperties'

        # check that all fields were identified as complex fields
        for prop in properties:
            assert isinstance(prop, ComplexField)

        # check that all field names were parsed correctly
        expected_names = ('Text Property', 'Number Property', 'Text Property')
        for name, prop in zip(expected_names, properties):
            assert name == prop.name

        # check that begin, separate and end were identified correctly
        attrib_key = '{http://schemas.openxmlformats.org/wordprocessingml/2006/main}fldCharType'
        expected_indexes = ((1, 3, 11), (13, 15, 17), (25, 27, 32))
        for prop, indexes in zip(properties, expected_indexes):
            assert prop.begin_run.getchildren()[1].attrib[attrib_key] == "begin"
            assert prop.get_separate_run().getchildren()[1].attrib[attrib_key] == "separate"
            assert prop.end_run.getchildren()[1].attrib[attrib_key] == "end"
            assert prop.w_p.index(prop.begin_run) == indexes[0]
            assert prop.w_p.index(prop.get_separate_run()) == indexes[1]
            assert prop.w_p.index(prop.end_run) == indexes[2]

def _find_docprops_in(self, element, name=None):
        # First we search for the simple fields:
        sfield_nodes = xpath(
            element,
            u'.//w:fldSimple[contains(@w:instr, \'DOCPROPERTY \')]')

        docprops = [SimpleField(sfield_node) for sfield_node in sfield_nodes]

        # Now for the complex fields
        cfield_nodes = xpath(
            element,
            u'.//w:instrText[contains(.,\'DOCPROPERTY \')]')

        docprops.extend([ComplexField(cfield_node) for cfield_node in cfield_nodes])

        if name is not None:
            docprops = filter(lambda prop: prop.name == name, docprops)
        return docprops

def __init__(self, field_node):
        super(ComplexField, self).__init__(field_node)
        # run and paragraph containing the field
        self.w_r = self.node.getparent()
        self.w_p = self.w_r.getparent()