DistinctOnTests.setUp() breaks when DatabaseFeature.ignores_nulls_in_unique_constraints = True

[Michael Manfre]

Django-mssql doesn't implement can_distinct_on_fields, but the DistinctOnTests fail because the test setUp creates Celebrity records without specifying a value for a nullable field that has a unique constraint. Any database backend with ignores_nulls_in_unique_constraints = False will error on this setup, even if they would skip the tests.

I'm not in a position to run these tests to determine if the greatest_fan value can be set to something other than NULL.

[Michael Manfre]

It might be worth wrapping setUp(), or the entire class with a can_distinct_on_fields check to avoid doing the test prep work for every backend other than postgresql_psycopg2.

[Anssi Kääriäinen]

Wrapping the whole class seems like the correct solution to me.

[Michael Manfre]

​https://github.com/django/django/pull/1622

[Michael Manfre <mmanfre@…>]

In 018037736fe575307f5331ebb4b126a0c886ecef:

Fixed #21099 - Skip DistinctOnTests unless backend can_distinct_on_fields

[Claude Paroz <claude@…>]

In e4c6fca6d21f6a6d16bd69d86928270b4d2d38fb:

Merge pull request #1622 from manfre/ticket-21099

Fixed #21099 - Skip DistinctOnTests unless backend can_distinct_on_field...