test/parallel/test-fs-write-sync.js

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'use strict';
require('../common');
const assert = require('assert');
const fs = require('fs');
const tmpdir = require('../common/tmpdir');
const filename = tmpdir.resolve('write.txt');

tmpdir.refresh();

{
  const parameters = [Buffer.from('bár'), 0, Buffer.byteLength('bár')];

  // The first time fs.writeSync is called with all parameters provided.
  // After that, each pop in the cycle removes the final parameter. So:
  // - The 2nd time fs.writeSync with a buffer, without the length parameter.
  // - The 3rd time fs.writeSync with a buffer, without the offset and length
  //   parameters.
  while (parameters.length > 0) {
    const fd = fs.openSync(filename, 'w');

    let written = fs.writeSync(fd, '');
    assert.strictEqual(written, 0);

    fs.writeSync(fd, 'foo');

    written = fs.writeSync(fd, ...parameters);
    assert.ok(written > 3);
    fs.closeSync(fd);

    assert.strictEqual(fs.readFileSync(filename, 'utf-8'), 'foobár');

    parameters.pop();
  }
}