incompatible with pytest-rerunfailures

[david-vankampen]

During testing of pytest-azurepipelines, which relies on pytest-nunit, it was found that if you have pytest-rerunfailures installed and use the reruns argument, then this plugin's self.nunit_xml.cases becomes empty, so the add attachment fixture raises a KeyError exception.

Minimal example:

def test_example(add_nunit_attachment):
    add_nunit_attachment("test_minimal.py", "test attachment")

And if you run this command:

pytest --nunit-xml=test-results.xml

then it will generate the report with attachment details as expected.

However, if you pip install pytest-rerunfailures, and then run:

pytest --nunit-xml=test-results.xml --reruns 0

then you get KeyError: 'test_minimal.py::test_example'