# Preval test case

# Hello world

> simple
>
> This is a simple test case as proof of concept

## Input

Each code fence uses quintuple ticks, has `js` as the first word, and is followed by the virtual path of that code block.
Other files can import that code by that name verbatim.
The `./intro.mjs` file is the standard entry point and should always exist. Anything else is optional.


The `$` symbol is special for testing and acts as a function with side effects. It will not be eliminated and in
tests we can use it to verify the result is still sound, despite any transformations.

`````js filename=./intro.mjs
import {f} from './foo.mjs';

const str = f();

$(str);
`````

`````js filename=./foo.js
export function f() {
  return "Hello, world!";
}
`````

## Output

`````js filename=./intro.mjs
$('Hello, world!')
`````

`````js filename=./intro.mjs
`````