Test Coverage Strategy

Coverage Priority Matrix

# Priority 1 — MUST be covered (>90%):
# - services.py (business logic)
# - download_service.py (financial/gating logic)
# - models.py (validation, clean, save overrides)

# Priority 2 — SHOULD be covered (>70%):
# - views.py (request handling)
# - api.py (API endpoints)
# - forms.py (validation)

# Priority 3 — NICE to cover (>50%):
# - tasks.py (Celery tasks)
# - middleware (request/response processing)
# - templatetags (display logic)

# OK to exclude:
# - migrations (auto-generated)
# - admin.py (Django admin config — low risk)
# - __init__.py (empty / re-exports)

Identifying Coverage Gaps

@pytest.mark.django_db
def test_gap_analysis():
    """Run this to identify critical untested paths."""
    from apps.firmwares.models import Firmware
    # Ensure model __str__ is tested
    fw = Firmware(version="1.0.0")
    assert str(fw)

    # Ensure model clean() is tested
    from django.core.exceptions import ValidationError
    fw_invalid = Firmware()
    try:
        fw_invalid.full_clean()
    except ValidationError:
        pass  # Expected — validates required fields

Meaningful Coverage vs Line Coverage

# BAD — high coverage, low value:
def test_model_exists():
    from apps.firmwares.models import Firmware
    assert Firmware  # Just imports the class

# GOOD — tests actual behavior:
@pytest.mark.django_db
def test_firmware_slug_generation():
    from tests.factories import FirmwareFactory
    fw = FirmwareFactory(version="3.2.1")
    assert fw.slug  # Auto-generated slug
    assert "3-2-1" in fw.slug or fw.slug != ""

Red Flags

• Counting coverage without --cov-branch — misses untested branches
• Padding coverage with trivial import tests — inflates numbers meaninglessly
• Excluding entire modules from coverage — hides critical gaps
• Setting fail_under too low — coverage ratchet should only go up

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