Build a normalization pipeline and check it against your harness

The exported snippets include a self-check over the test vectors. Run the snippet in your environment to verify it matches.

Python

# Normalization pipeline, library version 1. Steps: (none).
import re
import string
import unicodedata

def normalize(s):
    return s

def matches(expected, output):
    return normalize(output) == normalize(expected)

VECTORS = [
    ('\ufeffx', '\ufeffx'),
    ('\u0085x\u001c', '\u0085x\u001c'),
    ('\u00a0x ', '\u00a0x '),
    ('\u200bx', '\u200bx'),
    ('a\u0085b', 'a\u0085b'),
    ('a\ufeffb', 'a\ufeffb'),
    ('a \t\n b', 'a \t\n b'),
    ('wrong_item.\n', 'wrong_item.\n'),
    ('wrong_item.!', 'wrong_item.!'),
    ('a\u00f1adir a cart', 'a\u00f1adir a cart'),
    ('the cat', 'the cat'),
    ('An apple', 'An apple'),
    ('\u0130', '\u0130'),
    ('\u039f\u0394\u039f\u03a3', '\u039f\u0394\u039f\u03a3'),
    ('\u1e9e', '\u1e9e'),
    ('caf\u00e9!', 'caf\u00e9!'),
    ('\u00bfqu\u00e9?', '\u00bfqu\u00e9?'),
    ('\u00bfD\u00f3nde est\u00e1?', '\u00bfD\u00f3nde est\u00e1?'),
    ('\ufb01\uff21\uff22\uff23\u00b2', '\ufb01\uff21\uff22\uff23\u00b2'),
    ('P\u00e9rez', 'P\u00e9rez'),
    ('refund - status', 'refund - status'),
    ('"return_eligible"', '"return_eligible"'),
    ('\u201cescalate\u201d', '\u201cescalate\u201d'),
    ('"', '"'),
    ('```json\n{"a":1}\n```', '```json\n{"a":1}\n```'),
    ('```\n{"a":1}```', '```\n{"a":1}```'),
    ('Stra\u00dfe', 'Stra\u00dfe'),
]

if __name__ == '__main__':
    for i, (given, want) in enumerate(VECTORS):
        got = normalize(given)
        assert got == want, f'vector {i}: {given!r} gave {got!r}, expected {want!r}'
    print(f'{len(VECTORS)} vectors match')

TypeScript

// Normalization pipeline, library version 1. Steps: (none).
const PY_WS = '[\\t\\n\\u000B\\f\\r\\u001C-\\u001F \\u0085\\u00A0\\u1680\\u2000-\\u200A\\u2028\\u2029\\u202F\\u205F\\u3000]';
export function normalize(input: string): string {
  let s = input;
  return s;
}
export function matches(expected: string, output: string): boolean {
  return normalize(output) === normalize(expected);
}
export const VECTORS: [string, string][] = [
  ['\ufeffx', '\ufeffx'],
  ['\u0085x\u001c', '\u0085x\u001c'],
  ['\u00a0x ', '\u00a0x '],
  ['\u200bx', '\u200bx'],
  ['a\u0085b', 'a\u0085b'],
  ['a\ufeffb', 'a\ufeffb'],
  ['a \t\n b', 'a \t\n b'],
  ['wrong_item.\n', 'wrong_item.\n'],
  ['wrong_item.!', 'wrong_item.!'],
  ['a\u00f1adir a cart', 'a\u00f1adir a cart'],
  ['the cat', 'the cat'],
  ['An apple', 'An apple'],
  ['\u0130', '\u0130'],
  ['\u039f\u0394\u039f\u03a3', '\u039f\u0394\u039f\u03a3'],
  ['\u1e9e', '\u1e9e'],
  ['caf\u00e9!', 'caf\u00e9!'],
  ['\u00bfqu\u00e9?', '\u00bfqu\u00e9?'],
  ['\u00bfD\u00f3nde est\u00e1?', '\u00bfD\u00f3nde est\u00e1?'],
  ['\ufb01\uff21\uff22\uff23\u00b2', '\ufb01\uff21\uff22\uff23\u00b2'],
  ['P\u00e9rez', 'P\u00e9rez'],
  ['refund - status', 'refund - status'],
  ['"return_eligible"', '"return_eligible"'],
  ['\u201cescalate\u201d', '\u201cescalate\u201d'],
  ['"', '"'],
  ['```json\n{"a":1}\n```', '```json\n{"a":1}\n```'],
  ['```\n{"a":1}```', '```\n{"a":1}```'],
  ['Stra\u00dfe', 'Stra\u00dfe'],
];
export function selfCheck(): number[] {
  return VECTORS.flatMap(([given, want], i) => (normalize(given) === want ? [] : [i]));
}

Test vectors

[
  [
    "x",
    "x"
  ],
  [
    "…x\u001c",
    "…x\u001c"
  ],
  [
    " x ",
    " x "
  ],
  [
    "​x",
    "​x"
  ],
  [
    "a…b",
    "a…b"
  ],
  [
    "ab",
    "ab"
  ],
  [
    "a \t\n b",
    "a \t\n b"
  ],
  [
    "wrong_item.\n",
    "wrong_item.\n"
  ],
  [
    "wrong_item.!",
    "wrong_item.!"
  ],
  [
    "añadir a cart",
    "añadir a cart"
  ],
  [
    "the cat",
    "the cat"
  ],
  [
    "An apple",
    "An apple"
  ],
  [
    "İ",
    "İ"
  ],
  [
    "ΟΔΟΣ",
    "ΟΔΟΣ"
  ],
  [
    "ẞ",
    "ẞ"
  ],
  [
    "café!",
    "café!"
  ],
  [
    "¿qué?",
    "¿qué?"
  ],
  [
    "¿Dónde está?",
    "¿Dónde está?"
  ],
  [
    "fiＡＢＣ²",
    "fiＡＢＣ²"
  ],
  [
    "Pérez",
    "Pérez"
  ],
  [
    "refund - status",
    "refund - status"
  ],
  [
    "\"return_eligible\"",
    "\"return_eligible\""
  ],
  [
    "“escalate”",
    "“escalate”"
  ],
  [
    "\"",
    "\""
  ],
  [
    "```json\n{\"a\":1}\n```",
    "```json\n{\"a\":1}\n```"
  ],
  [
    "```\n{\"a\":1}```",
    "```\n{\"a\":1}```"
  ],
  [
    "Straße",
    "Straße"
  ]
]