Use table driven tests for many inputs to the same logic

When the same behaviour needs checking with many inputs, copy pasting a test ten times hides the one line that differs. Every major runner supports parametrized tests: test.each in Vitest and Jest, @pytest.mark.parametrize in pytest, subtests with a table in Go.

Each row becomes its own test in the report, so a failure tells you exactly which input broke. Adding a new edge case is one new line.

Keep the table readable: put the input and expected output side by side, and give rows an id when the values alone do not explain the case.

import pytest
from shipping import shipping_cost

@pytest.mark.parametrize(
    "weight_kg, expected",
    [
        (0.5, 200),   # small parcel
        (1.0, 200),   # boundary: still small
        (1.01, 350),  # just over the boundary
        (20.0, 900),  # largest allowed
    ],
)
def test_shipping_cost_by_weight(weight_kg, expected):
    assert shipping_cost(weight_kg) == expected


def test_rejects_weight_over_limit():
    with pytest.raises(ValueError):
        shipping_cost(20.5)