Parametrizing with subTest

Testing a function against twenty inputs by copy-pasting twenty methods is noise. subTest runs a loop of cases inside one test method — and keeps going after a failure so you see every broken case at once:

import unittest

class TestParse(unittest.TestCase):
    def test_parse_counts(self):
        cases = [
            ("42", 42),        # plain
            ("  7 ", 7),       # whitespace
            ("0", 0),          # zero
        ]
        for text, expected in cases:
            with self.subTest(text=text):
                self.assertEqual(parse_count(text), expected)

Without subTest, the first bad case hides the rest. With it, one run shows text=' 7 ' failed AND text='0' failed — the full picture in a single run. This is unittest's native answer to pytest's parametrize (pytest is the ecosystem favorite; its shape transfers directly).

Edge cases deserve explicit rows

Keep a mental checklist as you write the case list: empty, zero, one, negative, huge, unicode, whitespace, wrong type. Each becomes one row. A case list is also executable documentation of what your function accepts.