Crash in one test when switching to pytest

[vinitkumar]

Recently decided to use pytest fully and discovered this failure in test.

=================================== FAILURES ===================================
[52](https://github.com/vinitkumar/json2xml/runs/7473036610?check_suite_focus=true#step:5:53)
__________________ TestDict2xml.test_dict2xml_str_list_header __________________
[53](https://github.com/vinitkumar/json2xml/runs/7473036610?check_suite_focus=true#step:5:54)
[54](https://github.com/vinitkumar/json2xml/runs/7473036610?check_suite_focus=true#step:5:55)
self = <tests.test_dict2xml.TestDict2xml object at 0x7f687bd951d0>
[55](https://github.com/vinitkumar/json2xml/runs/7473036610?check_suite_focus=true#step:5:56)
[56](https://github.com/vinitkumar/json2xml/runs/7473036610?check_suite_focus=true#step:5:57)
    def test_dict2xml_str_list_header(self):
[57](https://github.com/vinitkumar/json2xml/runs/7473036610?check_suite_focus=true#step:5:58)
        from json2xml.dicttoxml import dict2xml_str
[58](https://github.com/vinitkumar/json2xml/runs/7473036610?check_suite_focus=true#step:5:59)
        item_func = dicttoxml.default_item_func
[59](https://github.com/vinitkumar/json2xml/runs/7473036610?check_suite_focus=true#step:5:60)
        item = {'frame_color': 'red'}
[60](https://github.com/vinitkumar/json2xml/runs/7473036610?check_suite_focus=true#step:5:61)
        parent = 'Bike'
[61](https://github.com/vinitkumar/json2xml/runs/7473036610?check_suite_focus=true#step:5:62)
        xml_str = dict2xml_str(attr_type=False, attr={}, item=item, item_func=item_func,
[62](https://github.com/vinitkumar/json2xml/runs/7473036610?check_suite_focus=true#step:5:63)
                               cdata=False, item_name='item', item_wrap=False, parentIsList=True,
[63](https://github.com/vinitkumar/json2xml/runs/7473036610?check_suite_focus=true#step:5:64)
                               parent=parent, list_headers=True)
[64](https://github.com/vinitkumar/json2xml/runs/7473036610?check_suite_focus=true#step:5:65)
[65](https://github.com/vinitkumar/json2xml/runs/7473036610?check_suite_focus=true#step:5:66)
>       assert f'{"<Bike><frame_color>red</frame_color></Bike>"}' == xml_str
[66](https://github.com/vinitkumar/json2xml/runs/7473036610?check_suite_focus=true#step:5:67)
E       assert '<Bike><frame...color></Bike>' == '<Bike><frame...color></Bike>'
[67](https://github.com/vinitkumar/json2xml/runs/7473036610?check_suite_focus=true#step:5:68)
E         - <Bike><frame_color id="item_464503">red</frame_color></Bike>
[68](https://github.com/vinitkumar/json2xml/runs/7473036610?check_suite_focus=true#step:5:69)
E         ?                   -----------------
[69](https://github.com/vinitkumar/json2xml/runs/7473036610?check_suite_focus=true#step:5:70)
E         + <Bike><frame_color>red</frame_color></Bike>

Which doesn't happen when the test is run isolated. It means one of the other tests is affecting this particular tests.

Curious about this, I commented most of the tests except test_get_unique_id
and voilà, it does cause this test to fail.

On a closer look, it does seem that we are using a global IDs list that gets mutated and shared across these two tests.

[vinitkumar]

Closed via #149