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Make sample messages with @cosyte/synth

A channel's tests need inputs that look like what the sending system produces. @cosyte/synth generates them: synthetic messages, built through the same parser Pathways uses, with names, identifiers and dates that belong to nobody. With a fixed seed it generates the same bytes on every machine and every run, so the inputs can be committed and regenerated without a difference.

You need a project made by pathways init, such as the one from the quickstart. Every command runs in its folder.

A copied real message is PHI. Never put a message from a live system in tests/, not even one with the names changed. It is patient data: once committed, it is in the repository's history, every clone and every CI log that prints it. Generate inputs, or write them by hand with values that are plainly invented.

1. Install the generator at a pinned minor​

npm install --save-dev @cosyte/synth@~0.1.5

The ~ keeps the generator on the 0.1 line. Below 1.0, a new minor version may change what a seed generates, and the inputs would change with it. Move to a new version on purpose: run the script again and read the difference before you commit it. Pathways already installs @cosyte/hl7, the parser the HL7 v2 generator builds with.

2. Generate the inputs with a fixed seed​

Create scripts/make-samples.mjs. It writes a synthetic admission (ADT^A01) and a synthetic update (ADT^A08) into the starter channel's tests/ folder:

scripts/make-samples.mjs
import { writeFileSync } from "node:fs";

import { generateAdt, roundTrip } from "@cosyte/synth/hl7";

// A fixed seed: the same messages on every machine and every run. Change it only on purpose.
const SEED = 20261111;
const TESTS = "channels/adt-to-lab/tests";

for (const trigger of ["A01", "A08"]) {
  const message = roundTrip(generateAdt({ seed: SEED, trigger }));
  if (!message.specClean) throw new Error(`the ${trigger} sample did not re-parse cleanly`);
  writeFileSync(`${TESTS}/synth-${trigger.toLowerCase()}.hl7`, message.content);
}
node scripts/make-samples.mjs

It writes synth-a01.hl7 and synth-a08.hl7. Run it again and the files do not change.

3. Save the expected outputs once​

npx pathways test adt-to-lab --update
UPDATED adt-to-lab/tests/a01.hl7 -> a01.expected.hl7
UPDATED adt-to-lab/tests/a08.hl7 -> a08.expected.hl7
UPDATED adt-to-lab/tests/synth-a01.hl7 -> synth-a01.expected.hl7
UPDATED adt-to-lab/tests/synth-a08.hl7 -> synth-a08.expected.hl7
0 passed, 0 failed, 4 updated

--update saves what the transform produces today; it checks nothing. Read each new expected file before you commit it. The starter transform keeps admissions and addresses them to the lab, so synth-a01.expected.hl7 is the admission with LAB in MSH-5, and synth-a08.expected.hl7 is empty, since the update is filtered out. The starter's own expected files come out as they were.

4. Commit the inputs and the reviewed expected files​

The expected file you read and committed is the check. From now on pathways test compares each output with it, byte for byte, so a change to the transform that changes an output fails until you save and review the new expected file:

npx pathways test adt-to-lab
PASS adt-to-lab/tests/a01.hl7
PASS adt-to-lab/tests/a08.hl7
PASS adt-to-lab/tests/synth-a01.hl7
PASS adt-to-lab/tests/synth-a08.hl7
4 passed, 0 failed

Commit scripts/make-samples.mjs, the generated inputs and their expected files. CI runs pathways test on the committed files; it does not run the script, so the inputs never change under a test.