`np.datetime64("NaT")` used in our tests without explicit unit is deprecated

[Simon-Will]

Description of the issue

When running the tests, I get the warnings below because np.datetime64("NaT") without an explicit time resolution is deprecated since NumPy 2.5.

tests/xml_download/test_utils_write_to_database.py::test_cast_date_columns_to_string
  /home/gorgor/Code/open-MaStR/tests/xml_download/test_utils_write_to_database.py:66: DeprecationWarning: The 'generic' unit for NumPy timedelta is deprecated, and will raise an error in the future. This includes implicit conversion of bare integers (e.g. `+ 1`).Please use a specific unit instead.
    np.datetime64("nat"),

tests/xml_download/test_utils_write_to_database.py::test_cast_date_columns_to_string
  /home/gorgor/Code/open-MaStR/tests/xml_download/test_utils_write_to_database.py:71: DeprecationWarning: The 'generic' unit for NumPy timedelta is deprecated, and will raise an error in the future. This includes implicit conversion of bare integers (e.g. `+ 1`).Please use a specific unit instead.
    np.datetime64("nat"),

tests/xml_download/test_utils_write_to_database.py::test_add_table_to_sqlite_database[add_table_to_sqlite_database]
tests/xml_download/test_utils_write_to_database.py::test_add_table_to_sqlite_database[add_table_to_sqlite_database]
tests/xml_download/test_utils_write_to_database.py::test_add_table_to_sqlite_database[add_table_to_non_sqlite_database]
tests/xml_download/test_utils_write_to_database.py::test_add_table_to_sqlite_database[add_table_to_non_sqlite_database]
  /home/gorgor/Code/open-MaStR/tests/xml_download/test_utils_write_to_database.py:294: DeprecationWarning: The 'generic' unit for NumPy timedelta is deprecated, and will raise an error in the future. This includes implicit conversion of bare integers (e.g. `+ 1`).Please use a specific unit instead.
    "Meldedatum": [np.datetime64("NaT"), np.datetime64("NaT")],

tests/xml_download/test_utils_write_to_database.py::test_add_table_to_sqlite_database[add_table_to_sqlite_database]
tests/xml_download/test_utils_write_to_database.py::test_add_table_to_sqlite_database[add_table_to_sqlite_database]
tests/xml_download/test_utils_write_to_database.py::test_add_table_to_sqlite_database[add_table_to_non_sqlite_database]
tests/xml_download/test_utils_write_to_database.py::test_add_table_to_sqlite_database[add_table_to_non_sqlite_database]
  /home/gorgor/Code/open-MaStR/tests/xml_download/test_utils_write_to_database.py:299: DeprecationWarning: The 'generic' unit for NumPy timedelta is deprecated, and will raise an error in the future. This includes implicit conversion of bare integers (e.g. `+ 1`).Please use a specific unit instead.
    "EegInbetriebnahmedatum": [np.datetime64("NaT"), np.datetime64("NaT")],

tests/xml_download/test_utils_write_to_database.py::test_add_table_to_sqlite_database[add_table_to_sqlite_database]
tests/xml_download/test_utils_write_to_database.py::test_add_table_to_sqlite_database[add_table_to_sqlite_database]
tests/xml_download/test_utils_write_to_database.py::test_add_table_to_sqlite_database[add_table_to_non_sqlite_database]
tests/xml_download/test_utils_write_to_database.py::test_add_table_to_sqlite_database[add_table_to_non_sqlite_database]
  /home/gorgor/Code/open-MaStR/tests/xml_download/test_utils_write_to_database.py:307: DeprecationWarning: The 'generic' unit for NumPy timedelta is deprecated, and will raise an error in the future. This includes implicit conversion of bare integers (e.g. `+ 1`).Please use a specific unit instead.
    "DatumDownload": [np.datetime64("NaT"), np.datetime64("NaT")],

Ideas of solution

We should just use np.datetime("NaT", "D") for places where we expect day resolution and np.datetime("NaT", "s") where we expect second resolution. We probably don't have other cases.

Workflow checklist

• I am aware of the workflow in CONTRIBUTING.md

[AdarshJ173]

Hi! I'd like to work on this fix.

The solution as described in the issue is straightforward — replace all bare np.datetime64("NaT") / np.datetime64("nat") calls in tests/xml_download/test_utils_write_to_database.py with explicit unit versions:

• np.datetime64("nat") for Date columns → np.datetime64("nat", "D")
• np.datetime64("nat") / np.datetime64("NaT") for DateTime columns → np.datetime64("NaT", "s")

This covers all 5 occurrences in the file. Opening a PR shortly!

[Solaris-star]

I'll take this good-first-issue and open a PR to pin explicit units on bare np.datetime64('NaT') usages in tests.

[FlorianK13]

The good first issue label seems to have some unexpected influence 😄