Test Migration Data

Testing Idempotent Data Migrations

@pytest.mark.django_db
def test_migration_is_idempotent():
    """Running the migration twice should not cause errors or duplicates."""
    from tests.factories import FirmwareFactory
    FirmwareFactory.create_batch(5)
    from apps.firmwares.models import Firmware
    count_before = Firmware.objects.count()
    # Simulate running the data migration function twice
    from apps.firmwares.migrations.0005_backfill_slugs import backfill_slugs
    from django.db import connection
    backfill_slugs(apps, connection.schema_editor())
    backfill_slugs(apps, connection.schema_editor())
    assert Firmware.objects.count() == count_before  # No duplicates

Testing Reverse Data Migration

@pytest.mark.django_db
def test_reverse_migration_clears_field():
    from tests.factories import FirmwareFactory
    fw = FirmwareFactory(slug="test-slug")
    # Simulate reverse
    from apps.firmwares.models import Firmware
    Firmware.objects.update(slug="")
    fw.refresh_from_db()
    assert fw.slug == ""

Testing Data Migration with Large Datasets

@pytest.mark.django_db
def test_batch_processing():
    """Data migrations should batch-process to avoid memory issues."""
    from tests.factories import FirmwareFactory
    FirmwareFactory.create_batch(100)
    from apps.firmwares.models import Firmware
    batch_size = 50
    total = Firmware.objects.count()
    processed = 0
    for i in range(0, total, batch_size):
        batch = Firmware.objects.all()[i:i + batch_size]
        for obj in batch:
            obj.slug = obj.version.replace(".", "-") if obj.version else "default"
            processed += 1
    assert processed == total

Testing Data Migration Edge Cases

@pytest.mark.django_db
@pytest.mark.parametrize("version,expected_slug", [
    ("1.0.0", "1-0-0"),
    ("", "default"),
    ("3.2.1-beta", "3-2-1-beta"),
])
def test_slug_generation(version, expected_slug):
    slug = version.replace(".", "-") if version else "default"
    assert slug == expected_slug

Red Flags

• Testing data migrations only via migrate command — too slow, test the function directly
• Not testing idempotency — migration may be run twice in some deployment scenarios
• Missing edge case tests — empty strings, None values, Unicode data
• Not batching updates in migration — OOM on large tables

Quality Gate

& .\.venv\Scripts\python.exe -m ruff check . --fix
& .\.venv\Scripts\python.exe -m ruff format .
& .\.venv\Scripts\python.exe manage.py check --settings=app.settings_dev