diff --git a/test/addons/repl-domain-abort/test.js b/test/addons/repl-domain-abort/test.js
index 969beec0d12442..1d0e5202b6a6f2 100644
--- a/test/addons/repl-domain-abort/test.js
+++ b/test/addons/repl-domain-abort/test.js
@@ -33,7 +33,7 @@ dInput._read = function _read(size) {
 };
 
 dOutput._write = function _write(chunk, encoding, cb) {
-  if (chunk.toString().indexOf('cb_ran') === 0)
+  if (chunk.toString().startsWith('cb_ran'))
     cb_ran = true;
   cb();
 };
diff --git a/test/disabled/test-sendfd.js b/test/disabled/test-sendfd.js
index 8de6045cb27d90..68d40993716093 100644
--- a/test/disabled/test-sendfd.js
+++ b/test/disabled/test-sendfd.js
@@ -74,7 +74,7 @@ pipeReadStream.on('data', function(data) {
     var rd = JSON.parse(d);
 
     assert.strictEqual(rd.pid, cpp);
-    assert.strictEqual(seenOrdinals.indexOf(rd.ord), -1);
+    assert.strictEqual(seenOrdinals.includes(rd.ord), false)
 
     seenOrdinals.unshift(rd.ord);
   });
diff --git a/test/doctool/test-doctool-html.js b/test/doctool/test-doctool-html.js
index b28d34b57e6edc..35fa921a3e9971 100644
--- a/test/doctool/test-doctool-html.js
+++ b/test/doctool/test-doctool-html.js
@@ -106,15 +106,15 @@ testData.forEach((item) => {
           const actual = output.replace(spaces, '');
           // Assert that the input stripped of all whitespace contains the
           // expected list
-          assert.notStrictEqual(actual.indexOf(expected), -1);
+          assert(actual.includes(expected));
 
           // Testing the insertion of Google Analytics script when
           // an analytics id is provided. Should not be present by default
           if (includeAnalytics) {
-            assert.notStrictEqual(actual.indexOf('google-analytics.com'), -1,
-                                  'Google Analytics script was not present');
+            assert(actual.includes('google-analytics.com'),
+                   'Google Analytics script was not present');
           } else {
-            assert.strictEqual(actual.indexOf('google-analytics.com'), -1,
+            assert.strictEqual(actual.includes('google-analytics.com'), false,
                                'Google Analytics script was present');
           }
         }));
diff --git a/test/internet/test-dns.js b/test/internet/test-dns.js
index ba40146c58342b..68365e59c107c3 100644
--- a/test/internet/test-dns.js
+++ b/test/internet/test-dns.js
@@ -360,7 +360,7 @@ TEST(function test_resolveTxt(done) {
     if (err) throw err;
     assert.strictEqual(records.length, 1);
     assert.ok(util.isArray(records[0]));
-    assert.strictEqual(records[0][0].indexOf('v=spf1'), 0);
+    assert(records[0][0].startsWith('v=spf1'));
     done();
   });
 
diff --git a/test/parallel/test-child-process-exec-cwd.js b/test/parallel/test-child-process-exec-cwd.js
index 95feb42314fc8d..d8d64776551278 100644
--- a/test/parallel/test-child-process-exec-cwd.js
+++ b/test/parallel/test-child-process-exec-cwd.js
@@ -15,5 +15,5 @@ if (common.isWindows) {
 
 exec(pwdcommand, {cwd: dir}, common.mustCall(function(err, stdout, stderr) {
   assert.ifError(err);
-  assert.strictEqual(stdout.indexOf(dir), 0);
+  assert(stdout.startsWith(dir));
 }));
diff --git a/test/parallel/test-console.js b/test/parallel/test-console.js
index 4618bbd28cf091..7d298674273ecf 100644
--- a/test/parallel/test-console.js
+++ b/test/parallel/test-console.js
@@ -115,8 +115,8 @@ assert.strictEqual("{ foo: 'bar', inspect: [Function: inspect] }\n",
                    strings.shift());
 assert.strictEqual("{ foo: 'bar', inspect: [Function: inspect] }\n",
                    strings.shift());
-assert.notStrictEqual(-1, strings.shift().indexOf('foo: [Object]'));
-assert.strictEqual(-1, strings.shift().indexOf('baz'));
+assert.ok(strings.shift().includes('foo: [Object]'));
+assert.strictEqual(strings.shift().includes('baz'), false);
 assert.ok(/^label: \d+\.\d{3}ms$/.test(strings.shift().trim()));
 assert.ok(/^__proto__: \d+\.\d{3}ms$/.test(strings.shift().trim()));
 assert.ok(/^constructor: \d+\.\d{3}ms$/.test(strings.shift().trim()));
diff --git a/test/parallel/test-dgram-error-message-address.js b/test/parallel/test-dgram-error-message-address.js
index 211adcffcc67b5..84b21d0f851347 100644
--- a/test/parallel/test-dgram-error-message-address.js
+++ b/test/parallel/test-dgram-error-message-address.js
@@ -26,7 +26,7 @@ socket_ipv6.on('listening', common.mustNotCall());
 socket_ipv6.on('error', common.mustCall(function(e) {
   // EAFNOSUPPORT or EPROTONOSUPPORT means IPv6 is disabled on this system.
   const allowed = ['EADDRNOTAVAIL', 'EAFNOSUPPORT', 'EPROTONOSUPPORT'];
-  assert.notStrictEqual(allowed.indexOf(e.code), -1);
+  assert(allowed.includes(e.code));
   assert.strictEqual(e.port, undefined);
   assert.strictEqual(e.message, `bind ${e.code} 111::1`);
   assert.strictEqual(e.address, '111::1');
diff --git a/test/parallel/test-domain-top-level-error-handler-throw.js b/test/parallel/test-domain-top-level-error-handler-throw.js
index 53a73eac426232..86df8db5b7423f 100644
--- a/test/parallel/test-domain-top-level-error-handler-throw.js
+++ b/test/parallel/test-domain-top-level-error-handler-throw.js
@@ -37,11 +37,8 @@ if (process.argv[2] === 'child') {
     });
 
     child.on('close', function onChildClosed() {
-      assert.notStrictEqual(
-        stderrOutput.indexOf(domainErrHandlerExMessage),
-        -1
-      );
-      assert.strictEqual(stderrOutput.indexOf(internalExMessage), -1);
+      assert(stderrOutput.includes(domainErrHandlerExMessage));
+      assert.strictEqual(stderrOutput.includes(internalExMessage), false);
     });
 
     child.on('exit', function onChildExited(exitCode, signal) {
diff --git a/test/parallel/test-domain-uncaught-exception.js b/test/parallel/test-domain-uncaught-exception.js
index 594cee542f80fb..bb6dd33e37b73a 100644
--- a/test/parallel/test-domain-uncaught-exception.js
+++ b/test/parallel/test-domain-uncaught-exception.js
@@ -190,7 +190,7 @@ if (process.argv[2] === 'child') {
 
       if (test.messagesReceived) {
         test.messagesReceived.forEach(function(receivedMessage) {
-          if (test.expectedMessages.indexOf(receivedMessage) === -1) {
+          if (!test.expectedMessages.includes(receivedMessage)) {
             assert(false, `test ${test.fn.name} should not have sent message: ${
                           receivedMessage} but did`);
           }
diff --git a/test/parallel/test-http-keepalive-maxsockets.js b/test/parallel/test-http-keepalive-maxsockets.js
index fd01fa02750853..de3bdea54f1f5d 100644
--- a/test/parallel/test-http-keepalive-maxsockets.js
+++ b/test/parallel/test-http-keepalive-maxsockets.js
@@ -7,7 +7,7 @@ const http = require('http');
 
 const serverSockets = [];
 const server = http.createServer(function(req, res) {
-  if (serverSockets.indexOf(req.socket) === -1) {
+  if (!serverSockets.includes(req.socket)) {
     serverSockets.push(req.socket);
   }
   res.end(req.url);
diff --git a/test/parallel/test-http-methods.js b/test/parallel/test-http-methods.js
index 6ba02807f8706b..fb49add6a2ad24 100644
--- a/test/parallel/test-http-methods.js
+++ b/test/parallel/test-http-methods.js
@@ -6,7 +6,7 @@ const util = require('util');
 
 assert(Array.isArray(http.METHODS));
 assert(http.METHODS.length > 0);
-assert.notStrictEqual(http.METHODS.indexOf('GET'), -1);
-assert.notStrictEqual(http.METHODS.indexOf('HEAD'), -1);
-assert.notStrictEqual(http.METHODS.indexOf('POST'), -1);
+assert(http.METHODS.includes('GET'));
+assert(http.METHODS.includes('HEAD'));
+assert(http.METHODS.includes('POST'));
 assert.deepStrictEqual(util._extend([], http.METHODS), http.METHODS.sort());
diff --git a/test/parallel/test-http-write-head.js b/test/parallel/test-http-write-head.js
index 2ceba8965c0ea4..c6b2a5e41ce820 100644
--- a/test/parallel/test-http-write-head.js
+++ b/test/parallel/test-http-write-head.js
@@ -46,7 +46,7 @@ function runTest() {
   http.get({ port: this.address().port }, common.mustCall((response) => {
     response.on('end', common.mustCall(() => {
       assert.strictEqual(response.headers['test'], '2');
-      assert.notStrictEqual(response.rawHeaders.indexOf('Test'), -1);
+      assert(response.rawHeaders.includes('Test'));
       s.close();
     }));
     response.resume();
diff --git a/test/parallel/test-net-server-connections.js b/test/parallel/test-net-server-connections.js
index 7ee1df1a544b95..491a97bddc3ffa 100644
--- a/test/parallel/test-net-server-connections.js
+++ b/test/parallel/test-net-server-connections.js
@@ -6,7 +6,6 @@ const net = require('net');
 
 // test that server.connections property is no longer enumerable now that it
 // has been marked as deprecated
-
 const server = new net.Server();
 
-assert.strictEqual(Object.keys(server).indexOf('connections'), -1);
+assert.strictEqual(Object.keys(server).includes('connections'), false);
diff --git a/test/parallel/test-path-parse-format.js b/test/parallel/test-path-parse-format.js
index f5d9881727f40f..a914f815410d2e 100644
--- a/test/parallel/test-path-parse-format.js
+++ b/test/parallel/test-path-parse-format.js
@@ -154,7 +154,7 @@ trailingTests.forEach(function(test) {
     if (!failed) {
       for (let i = 0; i < actualKeys.length; ++i) {
         const key = actualKeys[i];
-        if (expectedKeys.indexOf(key) === -1 || actual[key] !== expected[key]) {
+        if (!expectedKeys.includes(key) || actual[key] !== expected[key]) {
           failed = true;
           break;
         }
diff --git a/test/parallel/test-process-getgroups.js b/test/parallel/test-process-getgroups.js
index 390f188cf5bf4d..fae363e2196628 100644
--- a/test/parallel/test-process-getgroups.js
+++ b/test/parallel/test-process-getgroups.js
@@ -24,7 +24,7 @@ if (typeof process.getgroups === 'function') {
 }
 
 function check(a, b) {
-  for (let i = 0; i < a.length; ++i) assert.notStrictEqual(b.indexOf(a[i]), -1);
+  for (let i = 0; i < a.length; ++i) assert(b.includes(a[i]));
 }
 
 function unique(groups) {
diff --git a/test/parallel/test-repl-tab-complete.js b/test/parallel/test-repl-tab-complete.js
index e2b9b363fa53c6..11858564ef1035 100644
--- a/test/parallel/test-repl-tab-complete.js
+++ b/test/parallel/test-repl-tab-complete.js
@@ -186,7 +186,7 @@ putIn.run(['.clear']);
 testMe.complete('require(\'', common.mustCall(function(error, data) {
   assert.strictEqual(error, null);
   repl._builtinLibs.forEach(function(lib) {
-    assert.notStrictEqual(data[0].indexOf(lib), -1, `${lib} not found`);
+    assert(data[0].includes(lib), `${lib} not found`);
   });
 }));
 
@@ -194,7 +194,7 @@ testMe.complete('require(\'n', common.mustCall(function(error, data) {
   assert.strictEqual(error, null);
   assert.strictEqual(data.length, 2);
   assert.strictEqual(data[1], 'n');
-  assert.notStrictEqual(data[0].indexOf('net'), -1);
+  assert(data[0].includes('net'));
   // It's possible to pick up non-core modules too
   data[0].forEach(function(completion) {
     if (completion)
@@ -239,9 +239,9 @@ putIn.run(['.clear']);
 
 putIn.run(['var ary = [1,2,3];']);
 testMe.complete('ary.', common.mustCall(function(error, data) {
-  assert.strictEqual(data[0].indexOf('ary.0'), -1);
-  assert.strictEqual(data[0].indexOf('ary.1'), -1);
-  assert.strictEqual(data[0].indexOf('ary.2'), -1);
+  assert.strictEqual(data[0].includes('ary.0'), false);
+  assert.strictEqual(data[0].includes('ary.1'), false);
+  assert.strictEqual(data[0].includes('ary.2'), false);
 }));
 
 // Make sure tab completion does not include integer keys in an object
@@ -249,9 +249,9 @@ putIn.run(['.clear']);
 putIn.run(['var obj = {1:"a","1a":"b",a:"b"};']);
 
 testMe.complete('obj.', common.mustCall(function(error, data) {
-  assert.strictEqual(data[0].indexOf('obj.1'), -1);
-  assert.strictEqual(data[0].indexOf('obj.1a'), -1);
-  assert.notStrictEqual(data[0].indexOf('obj.a'), -1);
+  assert.strictEqual(data[0].includes('obj.1'), false);
+  assert.strictEqual(data[0].includes('obj.1a'), false);
+  assert(data[0].includes('obj.a'));
 }));
 
 // Don't try to complete results of non-simple expressions
@@ -265,9 +265,9 @@ putIn.run(['.clear']);
 putIn.run(['var obj = {1:"a","1a":"b",a:"b"};']);
 
 testMe.complete(' obj.', common.mustCall((error, data) => {
-  assert.strictEqual(data[0].indexOf('obj.1'), -1);
-  assert.strictEqual(data[0].indexOf('obj.1a'), -1);
-  assert.notStrictEqual(data[0].indexOf('obj.a'), -1);
+  assert.strictEqual(data[0].includes('obj.1'), false);
+  assert.strictEqual(data[0].includes('obj.1a'), false);
+  assert(data[0].includes('obj.a'));
 }));
 
 // Works inside assignments
diff --git a/test/parallel/test-tls-interleave.js b/test/parallel/test-tls-interleave.js
index 60d778b77de268..1bbba9aff73d44 100644
--- a/test/parallel/test-tls-interleave.js
+++ b/test/parallel/test-tls-interleave.js
@@ -38,7 +38,7 @@ const server = tls.createServer(options, function(c) {
 
       data = data.toString();
       while (data.length !== 0) {
-        assert.strictEqual(data.indexOf(writes[receivedWrites]), 0);
+        assert(data.startsWith(writes[receivedWrites]));
         data = data.slice(writes[receivedWrites].length);
 
         if (++receivedWrites === writes.length) {
diff --git a/test/pummel/test-dtrace-jsstack.js b/test/pummel/test-dtrace-jsstack.js
index ad58aaf7615081..9833324e072f93 100644
--- a/test/pummel/test-dtrace-jsstack.js
+++ b/test/pummel/test-dtrace-jsstack.js
@@ -65,14 +65,14 @@ dtrace.on('exit', function(code) {
   for (let i = 0; i < lines.length; i++) {
     const line = lines[i];
 
-    if (line.indexOf(sentinel) === -1 || frames.length === 0)
+    if (!line.includes(sentinel) || frames.length === 0)
       continue;
 
     const frame = line.substr(line.indexOf(sentinel) + sentinel.length);
     const top = frames.shift();
 
-    assert.strictEqual(frame.indexOf(top), 0,
-                       `unexpected frame where ${top} was expected`);
+    assert(frame.startsWith(top),
+           `unexpected frame where ${top} was expected`);
   }
 
   assert.strictEqual(frames.length, 0,
diff --git a/test/pummel/test-regress-GH-814.js b/test/pummel/test-regress-GH-814.js
index a3700c500b4f53..58ba57dc6c88e8 100644
--- a/test/pummel/test-regress-GH-814.js
+++ b/test/pummel/test-regress-GH-814.js
@@ -29,7 +29,7 @@ const tail = require('child_process').spawn('tail', ['-f', testFileName]);
 tail.stdout.on('data', tailCB);
 
 function tailCB(data) {
-  PASS = data.toString().indexOf('.') < 0;
+  PASS = !data.toString().includes('.');
 }
 
 
diff --git a/test/pummel/test-regress-GH-814_2.js b/test/pummel/test-regress-GH-814_2.js
index da315e3fc2b007..48f5de63efdc1c 100644
--- a/test/pummel/test-regress-GH-814_2.js
+++ b/test/pummel/test-regress-GH-814_2.js
@@ -13,7 +13,7 @@ const tailProc = require('child_process').spawn('tail', ['-f', testFileName]);
 tailProc.stdout.on('data', tailCB);
 
 function tailCB(data) {
-  PASS = data.toString().indexOf('.') < 0;
+  PASS = !data.toString().includes('.');
 
   if (PASS) {
     //console.error('i');