test: use const or let and assert.strictEqual

PR-URL: https://github.com/nodejs/node/pull/10001
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-fs-read-file-sync.js

@@ -1,13 +1,13 @@
 'use strict';
-var common = require('../common');
-var assert = require('assert');
-var path = require('path');
-var fs = require('fs');
+const common = require('../common');
+const assert = require('assert');
+const path = require('path');
+const fs = require('fs');
 
-var fn = path.join(common.fixturesDir, 'elipses.txt');
+const fn = path.join(common.fixturesDir, 'elipses.txt');
 
-var s = fs.readFileSync(fn, 'utf8');
-for (var i = 0; i < s.length; i++) {
-  assert.equal('\u2026', s[i]);
+const s = fs.readFileSync(fn, 'utf8');
+for (let i = 0; i < s.length; i++) {
+  assert.strictEqual('\u2026', s[i]);
 }
-assert.equal(10000, s.length);
+assert.strictEqual(10000, s.length);