test: use ES2017 syntax in test-fs-open-*

Update test-fs-open-flags to take advantage of destructuring and default
values.

Update test-fs-open-mode-mask to use a ternary to make use of a
constant possible.

PR-URL: #23031
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

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

@@ -29,15 +29,17 @@ const assert = require('assert');
 const fs = require('fs');
 const path = require('path');
 
-const O_APPEND = fs.constants.O_APPEND || 0;
-const O_CREAT = fs.constants.O_CREAT || 0;
-const O_EXCL = fs.constants.O_EXCL || 0;
-const O_RDONLY = fs.constants.O_RDONLY || 0;
-const O_RDWR = fs.constants.O_RDWR || 0;
-const O_SYNC = fs.constants.O_SYNC || 0;
-const O_DSYNC = fs.constants.O_DSYNC || 0;
-const O_TRUNC = fs.constants.O_TRUNC || 0;
-const O_WRONLY = fs.constants.O_WRONLY || 0;
+// 0 if not found in fs.constants
+const { O_APPEND = 0,
+        O_CREAT = 0,
+        O_EXCL = 0,
+        O_RDONLY = 0,
+        O_RDWR = 0,
+        O_SYNC = 0,
+        O_DSYNC = 0,
+        O_TRUNC = 0,
+        O_WRONLY = 0
+} = fs.constants;
 
 const { stringToFlags } = require('internal/fs/utils');
 

test/parallel/test-fs-open-mode-mask.js

@@ -7,13 +7,7 @@ const assert = require('assert');
 const path = require('path');
 const fs = require('fs');
 
-let mode;
-
-if (common.isWindows) {
-  mode = 0o444;
-} else {
-  mode = 0o644;
-}
+const mode = common.isWindows ? 0o444 : 0o644;
 
 const maskToIgnore = 0o10000;