test: fix redeclared vars in sequential tests

test/sequential/test-child-process-execsync.js

@@ -38,7 +38,7 @@ var msgBuf = new Buffer(msg + '\n');
 
 cmd = `"${process.execPath}" -e "console.log(\'${msg}\');"`;
 
-var ret = execSync(cmd);
+ret = execSync(cmd);
 
 assert.strictEqual(ret.length, msgBuf.length);
 assert.deepEqual(ret, msgBuf, 'execSync result buffer should match');

test/sequential/test-require-cache-without-stat.js

@@ -35,14 +35,14 @@ var counterBefore = counter;
 
 // Now load the module a bunch of times with equivalent paths.
 // stat should not be called.
-for (var i = 0; i < 100; i++) {
+for (let i = 0; i < 100; i++) {
   require(common.fixturesDir + '/a');
   require('../fixtures/a.js');
   require('./../fixtures/a.js');
 }
 
 // Do the same with a built-in module
-for (var i = 0; i < 100; i++) {
+for (let i = 0; i < 100; i++) {
   require('http');
 }
 

test/sequential/test-tcp-wrap-listen.js

@@ -38,8 +38,8 @@ server.onconnection = function(err, client) {
 
       var req = new WriteWrap();
       req.async = false;
-      var err = client.writeBuffer(req, buffer);
-      assert.equal(err, 0);
+      const returnCode = client.writeBuffer(req, buffer);
+      assert.equal(returnCode, 0);
       client.pendingWrites.push(req);
 
       console.log('client.writeQueueSize: ' + client.writeQueueSize);