Add tests with xfail for tracking presence of error elements

[jacobwegner]

refs #92 (comment)

Running the xfail tests tests via:

pytest -k test_no_errors --runxfail

Results in:

============================================ test session starts ============================================
platform darwin -- Python 3.10.11, pytest-7.2.2, pluggy-1.0.0
rootdir: macula-greek/test
collected 769 items / 715 deselected / 54 selected

test_nestle1904_lowfat.py ....F......................                                                 [ 50%]
test_sblgnt_lowfat.py ....FF.....................                                                     [100%]

================================================= FAILURES ==================================================
_____________________________ test_no_errors[../Nestle1904/lowfat/05-acts.xml] ______________________________

lowfat_file = '../Nestle1904/lowfat/05-acts.xml'

    @pytest.mark.xfail
    @pytest.mark.parametrize("lowfat_file", __lowfat_files__)
    def test_no_errors(lowfat_file):
        count = len(run_xpath_for_file(ERROR_EXPRESSION, lowfat_file))
>       assert count == 0
E       assert 1 == 0

test_nestle1904_lowfat.py:83: AssertionError
_______________________________ test_no_errors[../SBLGNT/lowfat/05-acts.xml] ________________________________

lowfat_file = '../SBLGNT/lowfat/05-acts.xml'

    @pytest.mark.xfail
    @pytest.mark.parametrize("lowfat_file", __sblgnt_lowfat_files__)
    def test_no_errors(lowfat_file):
        count = len(run_xpath_for_file(ERROR_EXPRESSION, lowfat_file))
>       assert count == 0
E       assert 1 == 0

test_sblgnt_lowfat.py:86: AssertionError
______________________________ test_no_errors[../SBLGNT/lowfat/06-romans.xml] _______________________________

lowfat_file = '../SBLGNT/lowfat/06-romans.xml'

    @pytest.mark.xfail
    @pytest.mark.parametrize("lowfat_file", __sblgnt_lowfat_files__)
    def test_no_errors(lowfat_file):
        count = len(run_xpath_for_file(ERROR_EXPRESSION, lowfat_file))
>       assert count == 0
E       assert 1 == 0

test_sblgnt_lowfat.py:86: AssertionError
========================================== short test summary info ==========================================
FAILED test_nestle1904_lowfat.py::test_no_errors[../Nestle1904/lowfat/05-acts.xml] - assert 1 == 0
FAILED test_sblgnt_lowfat.py::test_no_errors[../SBLGNT/lowfat/05-acts.xml] - assert 1 == 0
FAILED test_sblgnt_lowfat.py::test_no_errors[../SBLGNT/lowfat/06-romans.xml] - assert 1 == 0
=============================== 3 failed, 51 passed, 715 deselected in 3.08s ================================

[linear]

RND-26 Add additional unit tests for <error> element

[jacobwegner]

@jonathanrobie I've added the tests as requested; please take a look when you're able, and if all looks good, I can merge them in to main.

[jacobwegner]

(@jonathanrobie will try and create a new branch with a "manual" fix to the Lowfat, and I can help update the tests / pipeline at that point)