test/parallel/test-fs-truncate-clear-file-zero.js

// Copyright Joyent, Inc. and other Node contributors.
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'use strict';
const common = require('../common');
const tmpdir = require('../common/tmpdir');

// This test ensures that `fs.truncate` opens the file with `r+` and not `w`,
// which had earlier resulted in the target file's content getting zeroed out.
// https://github.com/nodejs/node-v0.x-archive/issues/6233

const assert = require('assert');
const fs = require('fs');

const filename = `${tmpdir.path}/truncate-file.txt`;

tmpdir.refresh();

// Synchronous test.
{
  fs.writeFileSync(filename, '0123456789');
  assert.strictEqual(fs.readFileSync(filename).toString(), '0123456789');
  fs.truncateSync(filename, 5);
  assert.strictEqual(fs.readFileSync(filename).toString(), '01234');
}

// Asynchronous test.
{
  fs.writeFileSync(filename, '0123456789');
  assert.strictEqual(fs.readFileSync(filename).toString(), '0123456789');
  fs.truncate(
    filename,
    5,
    common.mustSucceed(() => {
      assert.strictEqual(fs.readFileSync(filename).toString(), '01234');
    })
  );
}