Draw synthetic values for your own fixtures

When you build a fixture by hand, or in a format @cosyte/synth does not generate, the package root gives you the same seeded generator and value providers the format generators use. None of them needs a parser installed.

Create a seeded generator

createRng(seed) returns a generator. Every provider takes it as its first argument, so the values you draw depend only on the seed and the order you draw them in:

import { createRng, safe } from "@cosyte/synth";

const first = createRng(42);
const second = createRng(42);

safe.ssn(first) === safe.ssn(second); // => true
safe.phone(first) === safe.phone(second); // => true

The generator also has int(min, max), pick(items), bool(p), float(), and nextUint32() for your own choices. Draw from one generator in a fixed order, and a fixture regenerates the same way.

Draw the values

The providers are exported by name and grouped on safe:

Provider	Returns
ssn(rng)	a dashed SSN with an area from 900 to 999 and a group outside every ITIN range
ssn(rng, "advertising")	one of the ten values 987-00-4320 to 987-00-4329
phone(rng)	(AAA) 555-01NN, in the block reserved for fiction
email(rng, person?)	an address at example.com, example.org, or example.net
name(rng)	{ given, family } from the invented-name pool
address(rng)	{ street, city, state, zip } with an invented street and city and the ZIP Code 00000
identifier(rng, type?)	an ID of type MR (the default), AN, or MB under the assigning authority COSYTE-SYNTH
npi(rng)	10 digits whose check digit fails the NPI Luhn check
dea(rng, person?)	a DEA-shaped number whose check digit fails the DEA checksum
dateYmd(rng, min?, max?)	a YYYYMMDD date between 1930 and 2010 by default
ipv4(rng), ipv6(rng)	an address in a range reserved for documentation
uuid(rng)	a version 4 UUID drawn from the seed

import { createRng, isSyntheticEmail, safe } from "@cosyte/synth";

const rng = createRng(7);
const person = safe.name(rng);
const mrn = safe.identifier(rng, "MR");
const home = safe.address(rng);

mrn.assigningAuthority; // => "COSYTE-SYNTH"
home.zip; // => "00000"
isSyntheticEmail(safe.email(rng, person)); // => true

The floor table cites the authority behind each range, and says where no authority reserves one.

Check a value

The checks tell you whether a value falls in a synthetic range. Use them to assert that a fixture you built, or one a colleague committed, holds no value that could be real:

import { createRng, isItinFormatted, isSyntheticNpi, isSyntheticPhone, isSyntheticSsn, safe } from "@cosyte/synth";

const rng = createRng(1);
const nationalId = safe.ssn(rng);

isSyntheticSsn(nationalId); // => true
isItinFormatted(nationalId); // => false
isSyntheticNpi(safe.npi(rng)); // => true
isSyntheticPhone("555-0100"); // => true
isSyntheticPhone("555-1212"); // => false

The other checks are isSyntheticEmail, isSyntheticIp, and isSyntheticDea. npiCheckDigit, deaCheckDigit, and luhnMod10 compute the check digits behind them.

Use the name pools directly

The invented names are exported as SYNTHETIC_GIVEN_NAMES, SYNTHETIC_FAMILY_NAMES, SYNTHETIC_STREET_NAMES, and SYNTHETIC_CITY_NAMES, frozen arrays you can draw from with rng.pick:

import { SYNTHETIC_FAMILY_NAMES, createRng } from "@cosyte/synth";

const family = createRng(3).pick(SYNTHETIC_FAMILY_NAMES);

SYNTHETIC_FAMILY_NAMES.includes(family); // => true

Related

• Reference: createRng, safe, isSyntheticSsn, and Rng.
• How it works: why a seed gives the same values.