verify

name	verify
description	Verify netto library changes by driving the public package API end-to-end

Verifying netto changes

netto is a pure-Python library; its surface is the public package boundary (from netto import calc_netto, calc_inverse_netto, TaxConfig).

Handle

• pip install -e . (usually already installed; check with python -c "import netto; print(netto.__file__)").
• Drive it with a consumer script run from OUTSIDE the repo (e.g. the session scratchpad) so imports resolve through the installed package, plus python examples/examples.py from the repo root as the in-repo consumer.

Flows worth driving

• calc_netto across years (2018, 2022, 2025) and configs: single, married, partner_salary (dual income), verbose=True, church tax on/off.
• calc_inverse_netto roundtrip: calc_inverse_netto(calc_netto(x)) == x.
• Married invariants: netto(married) >= netto(single); household netto symmetric under swapping salary/partner_salary; soli 0 below the doubled Freigrenze.
• Children (num_children > 0): benefit vs has_children-only config is exactly Kindergeld at low income and strictly more at high income (Freibetrag wins the Guenstigerpruefung); netto(0 gross, kids) == Kindergeld.
• Error paths: negative salary/partner_salary, partner_salary without is_married, desired netto already covered by partner salary alone.

Gotchas

• ruff format . from the repo root also formats files in the cwd — run the consumer script from the scratchpad, not the repo.
• scipy emits an IntegrationWarning for very high incomes (>= ~300k); it is pre-existing and harmless.
• Cross-check income tax against the official formula: for married, calc_income_tax(zvE, married) must equal 2 * calc_income_tax(zvE/2, single) (calc_income_tax implements the exact BMF polynomial).