test: numeric flags to fs.open

This has been supperted for long but never tested nor documented.

PR-URL: #3641
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-fs-open-numeric-flags.js

@@ -0,0 +1,16 @@
+'use strict';
+const common = require('../common');
+
+const constants = require('constants');
+const assert = require('assert');
+const fs = require('fs');
+const path = require('path');
+
+common.refreshTmpDir();
+
+// O_WRONLY without O_CREAT shall fail with ENOENT
+const pathNE = path.join(common.tmpDir, 'file-should-not-exist');
+assert.throws(
+  () => fs.openSync(pathNE, constants.O_WRONLY),
+  (e) => e.code === 'ENOENT'
+);