Successfully writes to mock directories with 0555 mode

[furikake]

Expected

A mock directory set with 0555 mode should fail to write with EACCES error when attempting to write to a new file in that directory.

Actual

You can successfully write a new file.

Steps to Reproduce

This test shows the steps to reproduce.

'use strict';

const helper = require('../helper');
const fs = require('fs');
const mock = require('../../lib/index');

const assert = helper.assert;

describe('testing directory write permissions', function() {
  beforeEach(function() {
    mock({
      'mod/444': mock.directory({mode: 0o444}),
      'mod/555': mock.directory({mode: 0o555})
    });
  });
  afterEach(mock.restore);

  it('generates EACCES for W_OK and 555', function(done) {
    fs.access('mod/555', fs.W_OK, function(err) {
      assert.instanceOf(err, Error);
      assert.equal(err.code, 'EACCES');
      done();
    });
  });

  it('fails to write to dir with 0444 mode', function(done) {
    fs.writeFile('mod/444/should-fail', 'bar', 'utf8', function(err) {
      assert.instanceOf(err, Error);
      assert.equal(err.code, 'EACCES');
      done();
    });
  });

  it('fails to write to dir with 0555 mode', function(done) {
    fs.writeFile('mod/555/should-fail', 'bar', 'utf8', function(err) {
      if (err) {
        assert.instanceOf(err, Error);
        assert.equal(err.code, 'EACCES');
        return done(err);
      } else {
        const val = fs.readFileSync('mod/555/should-fail');
        assert.fail(`did not throw EACCES error - file contents: ${val}`);
        done();
      }
    });
  });
});

The output of the test

  1) testing directory write permissions
       fails to write to dir with 0555 mode:
     Uncaught AssertionError: did not throw EACCES error - file contents: bar
      at /Users/winston/dev/github/tschaub/mock-fs/test/lib/555.spec.js:42:16
      at FSReqCallback.oncomplete (fs.js:155:23)
      at /Users/winston/dev/github/tschaub/mock-fs/lib/binding.js:88:9
      at processTicksAndRejections (internal/process/task_queues.js:79:11)

[furikake]

I should also add that this happens on MacOS. Haven't tested on Linux