node/test/parallel/test-fs-read.js

'use strict';
const common = require('../common');
const assert = require('assert');
const path = require('path');
const fs = require('fs');
const filepath = path.join(common.fixturesDir, 'x.txt');
const fd = fs.openSync(filepath, 'r');
const expected = 'xyz\n';

fs.read(fd,
        expected.length,
        0,
        'utf-8',
        common.mustCall((err, str, bytesRead) => {
          assert.ifError(err);
          assert.strictEqual(str, expected);
          assert.strictEqual(bytesRead, expected.length);
        }));

var r = fs.readSync(fd, expected.length, 0, 'utf-8');
assert.strictEqual(r[0], expected);
assert.strictEqual(r[1], expected.length);