diff --git a/test/parallel/test-process-env.js b/test/parallel/test-process-env.js
index 932bae3f8ff095..b5e62324ac15db 100644
--- a/test/parallel/test-process-env.js
+++ b/test/parallel/test-process-env.js
@@ -31,12 +31,12 @@ if (process.argv[2] == 'you-are-the-child') {
   assert.equal(42, process.env.NODE_PROCESS_ENV);
   assert.equal('asdf', process.env.hasOwnProperty);
   var hasOwnProperty = Object.prototype.hasOwnProperty;
-  var has = hasOwnProperty.call(process.env, 'hasOwnProperty');
+  const has = hasOwnProperty.call(process.env, 'hasOwnProperty');
   assert.equal(true, has);
   process.exit(0);
 } else {
   assert.equal(Object.prototype.hasOwnProperty, process.env.hasOwnProperty);
-  var has = process.env.hasOwnProperty('hasOwnProperty');
+  const has = process.env.hasOwnProperty('hasOwnProperty');
   assert.equal(false, has);
 
   process.env.hasOwnProperty = 'asdf';
diff --git a/test/parallel/test-querystring.js b/test/parallel/test-querystring.js
index f30d0a3cb2597e..b4388852499ed1 100644
--- a/test/parallel/test-querystring.js
+++ b/test/parallel/test-querystring.js
@@ -148,29 +148,32 @@ assert.strictEqual('foo=', qs.stringify({ foo: NaN }));
 assert.strictEqual('foo=', qs.stringify({ foo: Infinity }));
 
 // nested
-var f = qs.stringify({
-  a: 'b',
-  q: qs.stringify({
-    x: 'y',
-    y: 'z'
-  })
-});
-assert.equal(f, 'a=b&q=x%3Dy%26y%3Dz');
+{
+  const f = qs.stringify({
+    a: 'b',
+    q: qs.stringify({
+      x: 'y',
+      y: 'z'
+    })
+  });
+  assert.equal(f, 'a=b&q=x%3Dy%26y%3Dz');
+}
 
 assert.doesNotThrow(function() {
   qs.parse(undefined);
 });
 
 // nested in colon
-var f = qs.stringify({
-  a: 'b',
-  q: qs.stringify({
-    x: 'y',
-    y: 'z'
-  }, ';', ':')
-}, ';', ':');
-assert.equal(f, 'a:b;q:x%3Ay%3By%3Az');
-
+{
+  const f = qs.stringify({
+    a: 'b',
+    q: qs.stringify({
+      x: 'y',
+      y: 'z'
+    }, ';', ':')
+  }, ';', ':');
+  assert.equal(f, 'a:b;q:x%3Ay%3By%3Az');
+}
 
 assert.deepEqual({}, qs.parse());
 
diff --git a/test/parallel/test-readline-interface.js b/test/parallel/test-readline-interface.js
index 9697b25ab54259..5e9842acb00084 100644
--- a/test/parallel/test-readline-interface.js
+++ b/test/parallel/test-readline-interface.js
@@ -296,7 +296,7 @@ function isWarned(emitter) {
     rli.question(expectedLines.join('\n'), function() {
       rli.close();
     });
-    var cursorPos = rli._getCursorPos();
+    cursorPos = rli._getCursorPos();
     assert.equal(cursorPos.rows, expectedLines.length - 1);
     assert.equal(cursorPos.cols, expectedLines.slice(-1)[0].length);
     rli.close();
diff --git a/test/parallel/test-repl-persistent-history.js b/test/parallel/test-repl-persistent-history.js
index 387cef7e97a794..e8b6d416f00ec4 100644
--- a/test/parallel/test-repl-persistent-history.js
+++ b/test/parallel/test-repl-persistent-history.js
@@ -272,11 +272,7 @@ function runTest(assertCleaned) {
     });
 
     function onClose() {
-      if (after) {
-        var cleaned = after();
-      } else {
-        var cleaned = cleanupTmpFile();
-      }
+      const cleaned = after ? after() : cleanupTmpFile();
 
       try {
         // Ensure everything that we expected was output
diff --git a/test/parallel/test-stream2-push.js b/test/parallel/test-stream2-push.js
index 99b73d7277aa52..e4603e688ecf55 100644
--- a/test/parallel/test-stream2-push.js
+++ b/test/parallel/test-stream2-push.js
@@ -10,7 +10,7 @@ var EE = require('events').EventEmitter;
 
 // a mock thing a bit like the net.Socket/tcp_wrap.handle interaction
 
-var stream = new Readable({
+stream = new Readable({
   highWaterMark: 16,
   encoding: 'utf8'
 });
diff --git a/test/parallel/test-string-decoder-end.js b/test/parallel/test-string-decoder-end.js
index c3afb88d778b39..a064250dcdd39f 100644
--- a/test/parallel/test-string-decoder-end.js
+++ b/test/parallel/test-string-decoder-end.js
@@ -43,7 +43,7 @@ function testBuf(encoding, buf) {
 
   // write the whole buffer at once.
   var res2 = '';
-  var s = new SD(encoding);
+  s = new SD(encoding);
   res2 += s.write(buf);
   res2 += s.end();
 
diff --git a/test/parallel/test-stringbytes-external.js b/test/parallel/test-stringbytes-external.js
index 1f03e2be42f577..f9bd78378e3414 100644
--- a/test/parallel/test-stringbytes-external.js
+++ b/test/parallel/test-stringbytes-external.js
@@ -22,9 +22,9 @@ write_str = Array(size).join(write_str);
 ucs2_control = Array(size).join(ucs2_control);
 
 // check resultant buffer and output string
-var b = new Buffer(write_str, 'ucs2');
+b = new Buffer(write_str, 'ucs2');
 // check fist Buffer created from write string
-for (var i = 0; i < b.length; i += 2) {
+for (let i = 0; i < b.length; i += 2) {
   assert.equal(b[i], 0x61);
   assert.equal(b[i + 1], 0);
 }
@@ -39,7 +39,7 @@ var c_ucs = new Buffer(b_ucs, 'ucs2');
 // make sure they're the same length
 assert.equal(c_bin.length, c_ucs.length);
 // make sure Buffers from externals are the same
-for (var i = 0; i < c_bin.length; i++) {
+for (let i = 0; i < c_bin.length; i++) {
   assert.equal(c_bin[i], c_ucs[i]);
 }
 // check resultant strings
diff --git a/test/parallel/test-tls-cipher-list.js b/test/parallel/test-tls-cipher-list.js
index f20a0a6a249aed..70c99dd91e439c 100644
--- a/test/parallel/test-tls-cipher-list.js
+++ b/test/parallel/test-tls-cipher-list.js
@@ -12,7 +12,7 @@ const defaultCoreList = require('constants').defaultCoreCipherList;
 
 function doCheck(arg, check) {
   var out = '';
-  var arg = arg.concat([
+  arg = arg.concat([
     '-pe',
     'require("constants").defaultCipherList'
   ]);
diff --git a/test/parallel/test-zlib.js b/test/parallel/test-zlib.js
index b3f193d0a60b2c..1256d94a61402d 100644
--- a/test/parallel/test-zlib.js
+++ b/test/parallel/test-zlib.js
@@ -42,7 +42,7 @@ var testFiles = ['person.jpg', 'elipses.txt', 'empty.txt'];
 
 if (process.env.FAST) {
   zlibPairs = [[zlib.Gzip, zlib.Unzip]];
-  var testFiles = ['person.jpg'];
+  testFiles = ['person.jpg'];
 }
 
 var tests = {};