diff --git a/test/parallel/test-child-process-stdout-flush-exit.js b/test/parallel/test-child-process-stdout-flush-exit.js
index b76a7cb5e5a8e2..9db74b51ce5864 100644
--- a/test/parallel/test-child-process-stdout-flush-exit.js
+++ b/test/parallel/test-child-process-stdout-flush-exit.js
@@ -1,23 +1,23 @@
 'use strict';
-var common = require('../common');
-var assert = require('assert');
+const common = require('../common');
+const assert = require('assert');
 
 // if child process output to console and exit
 if (process.argv[2] === 'child') {
   console.log('hello');
-  for (var i = 0; i < 200; i++) {
+  for (let i = 0; i < 200; i++) {
     console.log('filler');
   }
   console.log('goodbye');
   process.exit(0);
 } else {
   // parent process
-  var spawn = require('child_process').spawn;
+  const spawn = require('child_process').spawn;
 
   // spawn self as child
-  var child = spawn(process.argv[0], [process.argv[1], 'child']);
+  const child = spawn(process.argv[0], [process.argv[1], 'child']);
 
-  var stdout = '';
+  let stdout = '';
 
   child.stderr.setEncoding('utf8');
   child.stderr.on('data', function(data) {
@@ -32,7 +32,7 @@ if (process.argv[2] === 'child') {
   });
 
   child.on('close', common.mustCall(function() {
-    assert.equal(stdout.slice(0, 6), 'hello\n');
-    assert.equal(stdout.slice(stdout.length - 8), 'goodbye\n');
+    assert.strictEqual(stdout.slice(0, 6), 'hello\n');
+    assert.strictEqual(stdout.slice(stdout.length - 8), 'goodbye\n');
   }));
 }
diff --git a/test/parallel/test-crypto-cipher-decipher.js b/test/parallel/test-crypto-cipher-decipher.js
index c63bcd6f9e2695..e53f02edfa0c86 100644
--- a/test/parallel/test-crypto-cipher-decipher.js
+++ b/test/parallel/test-crypto-cipher-decipher.js
@@ -1,6 +1,5 @@
 'use strict';
-var common = require('../common');
-var assert = require('assert');
+const common = require('../common');
 
 if (!common.hasCrypto) {
   common.skip('missing crypto');
@@ -10,21 +9,22 @@ if (common.hasFipsCrypto) {
   common.skip('not supported in FIPS mode');
   return;
 }
-var crypto = require('crypto');
+const crypto = require('crypto');
+const assert = require('assert');
 
 function testCipher1(key) {
   // Test encryption and decryption
-  var plaintext = 'Keep this a secret? No! Tell everyone about node.js!';
-  var cipher = crypto.createCipher('aes192', key);
+  const plaintext = 'Keep this a secret? No! Tell everyone about node.js!';
+  const cipher = crypto.createCipher('aes192', key);
 
   // encrypt plaintext which is in utf8 format
   // to a ciphertext which will be in hex
-  var ciph = cipher.update(plaintext, 'utf8', 'hex');
+  let ciph = cipher.update(plaintext, 'utf8', 'hex');
   // Only use binary or hex, not base64.
   ciph += cipher.final('hex');
 
-  var decipher = crypto.createDecipher('aes192', key);
-  var txt = decipher.update(ciph, 'hex', 'utf8');
+  const decipher = crypto.createDecipher('aes192', key);
+  let txt = decipher.update(ciph, 'hex', 'utf8');
   txt += decipher.final('utf8');
 
   assert.strictEqual(txt, plaintext, 'encryption and decryption');
@@ -33,11 +33,11 @@ function testCipher1(key) {
   // NB: In real life, it's not guaranteed that you can get all of it
   // in a single read() like this.  But in this case, we know it's
   // quite small, so there's no harm.
-  var cStream = crypto.createCipher('aes192', key);
+  const cStream = crypto.createCipher('aes192', key);
   cStream.end(plaintext);
   ciph = cStream.read();
 
-  var dStream = crypto.createDecipher('aes192', key);
+  const dStream = crypto.createDecipher('aes192', key);
   dStream.end(ciph);
   txt = dStream.read().toString('utf8');
 
@@ -48,19 +48,19 @@ function testCipher1(key) {
 function testCipher2(key) {
   // encryption and decryption with Base64
   // reported in https://github.com/joyent/node/issues/738
-  var plaintext =
+  const plaintext =
       '32|RmVZZkFUVmpRRkp0TmJaUm56ZU9qcnJkaXNNWVNpTTU*|iXmckfRWZBGWWELw' +
       'eCBsThSsfUHLeRe0KCsK8ooHgxie0zOINpXxfZi/oNG7uq9JWFVCk70gfzQH8ZUJ' +
       'jAfaFg**';
-  var cipher = crypto.createCipher('aes256', key);
+  const cipher = crypto.createCipher('aes256', key);
 
   // encrypt plaintext which is in utf8 format
   // to a ciphertext which will be in Base64
-  var ciph = cipher.update(plaintext, 'utf8', 'base64');
+  let ciph = cipher.update(plaintext, 'utf8', 'base64');
   ciph += cipher.final('base64');
 
-  var decipher = crypto.createDecipher('aes256', key);
-  var txt = decipher.update(ciph, 'base64', 'utf8');
+  const decipher = crypto.createDecipher('aes256', key);
+  let txt = decipher.update(ciph, 'base64', 'utf8');
   txt += decipher.final('utf8');
 
   assert.strictEqual(txt, plaintext, 'encryption and decryption with Base64');
@@ -119,12 +119,12 @@ testCipher2(Buffer.from('0123456789abcdef'));
   const key = '0123456789abcdef';
   const plaintext = 'Top secret!!!';
   const c = crypto.createCipher('aes192', key);
-  var ciph = c.update(plaintext, 'utf16le', 'base64');
+  let ciph = c.update(plaintext, 'utf16le', 'base64');
   ciph += c.final('base64');
 
-  var decipher = crypto.createDecipher('aes192', key);
+  let decipher = crypto.createDecipher('aes192', key);
 
-  var txt;
+  let txt;
   assert.doesNotThrow(() => txt = decipher.update(ciph, 'base64', 'ucs2'));
   assert.doesNotThrow(() => txt += decipher.final('ucs2'));
   assert.strictEqual(txt, plaintext, 'decrypted result in ucs2');
diff --git a/test/parallel/test-https-timeout-server.js b/test/parallel/test-https-timeout-server.js
index 92b06f1495ddbf..04ccf0a64d2d7c 100644
--- a/test/parallel/test-https-timeout-server.js
+++ b/test/parallel/test-https-timeout-server.js
@@ -1,29 +1,29 @@
 'use strict';
-var common = require('../common');
-var assert = require('assert');
+const common = require('../common');
 
 if (!common.hasCrypto) {
   common.skip('missing crypto');
   return;
 }
-var https = require('https');
+const assert = require('assert');
+const https = require('https');
 
-var net = require('net');
-var fs = require('fs');
+const net = require('net');
+const fs = require('fs');
 
-var options = {
+const options = {
   key: fs.readFileSync(common.fixturesDir + '/keys/agent1-key.pem'),
   cert: fs.readFileSync(common.fixturesDir + '/keys/agent1-cert.pem'),
   handshakeTimeout: 50
 };
 
-var server = https.createServer(options, common.fail);
+const server = https.createServer(options, common.fail);
 
 server.on('clientError', common.mustCall(function(err, conn) {
   // Don't hesitate to update the asserts if the internal structure of
   // the cleartext object ever changes. We're checking that the https.Server
   // has closed the client connection.
-  assert.equal(conn._secureEstablished, false);
+  assert.strictEqual(conn._secureEstablished, false);
   server.close();
   conn.destroy();
 }));
diff --git a/test/parallel/test-tls-on-empty-socket.js b/test/parallel/test-tls-on-empty-socket.js
index 58bc101333a583..84e27c5dd3067e 100644
--- a/test/parallel/test-tls-on-empty-socket.js
+++ b/test/parallel/test-tls-on-empty-socket.js
@@ -1,27 +1,27 @@
 'use strict';
-var common = require('../common');
-var assert = require('assert');
+const common = require('../common');
 
 if (!common.hasCrypto) {
   common.skip('missing crypto');
   return;
 }
-var tls = require('tls');
+const assert = require('assert');
+const tls = require('tls');
 
-var fs = require('fs');
-var net = require('net');
+const fs = require('fs');
+const net = require('net');
 
-var out = '';
+let out = '';
 
-var server = tls.createServer({
+const server = tls.createServer({
   key: fs.readFileSync(common.fixturesDir + '/keys/agent1-key.pem'),
   cert: fs.readFileSync(common.fixturesDir + '/keys/agent1-cert.pem')
 }, function(c) {
   c.end('hello');
 }).listen(0, function() {
-  var socket = new net.Socket();
+  const socket = new net.Socket();
 
-  var s = tls.connect({
+  const s = tls.connect({
     socket: socket,
     rejectUnauthorized: false
   }, function() {
@@ -38,5 +38,5 @@ var server = tls.createServer({
 });
 
 process.on('exit', function() {
-  assert.equal(out, 'hello');
+  assert.strictEqual(out, 'hello');
 });