# Testing escape output

> Assert what your CLI writes on a supporting terminal and on a pipe by passing a literal runtime to emit() — no environment patching.

Source: https://paratext.interlace.tools/docs/recipes/testing-escapes

`emit` reads only the runtime it is handed, so a test asserts both outputs, on any machine and
in any CI, with two literals:

```js title="escapes-check.mjs"
import assert from 'node:assert/strict';

import { emit } from 'paratext';

const iterm = { env: { TERM_PROGRAM: 'iTerm.app' }, isTTY: { stdout: true } };
const pipe = { env: { TERM_PROGRAM: 'iTerm.app' }, isTTY: { stdout: false } };
const args = { text: 'Docs', url: 'https://x.dev' };

assert.equal(emit(iterm, 'link', args), '\u001B]8;;https://x.dev\u0007Docs\u001B]8;;\u0007');
assert.equal(emit(pipe, 'link', args), 'Docs (https://x.dev)');
assert.doesNotMatch(emit(pipe, 'notify', { title: 'Done' }), /[\u0000-\u001F]/u);

console.log('ok');
```

```text title="node escapes-check.mjs"
ok
```

The second runtime is iTerm2 with its output piped — a user redirecting to a file — and it gets
the projection, because `when: { tty: true }` refuses a pipe whatever the terminal program is.