test: remove common.noop

This change removes `common.noop` from the Node.js internal testing
common module.

Over the last few weeks, I've grown to dislike the `common.noop`
abstraction.

First, new (and experienced) contributors are unaware of it and so it
results in a large number of low-value nits on PRs. It also increases
the number of things newcomers and infrequent contributors have to be
aware of to be effective on the project.

Second, it is confusing. Is it a singleton/property or a getter? Which
should be expected? This can lead to subtle and hard-to-find bugs. (To
my knowledge, none have landed on master. But I also think it's only a
matter of time.)

Third, the abstraction is low-value in my opinion. What does it really
get us? A case could me made that it is without value at all.

Lastly, and this is minor, but the abstraction is wordier than not using
the abstraction. `common.noop` doesn't save anything over `() => {}`.

So, I propose removing it.

PR-URL: #12822
Backport-PR-URL: #14174
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Refael Ackermann <refack@gmail.com>

Author: Trott

Diff for: test/common/README.md

@@ -183,26 +183,26 @@ Gets IP of localhost
 Array of IPV6 hosts.
 
 ### mustCall([fn][, exact])
-* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) default = `common.noop`
+* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) default = () => {}
 * `exact` [<Number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) default = 1
 * return [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
 
 Returns a function that calls `fn`. If the returned function has not been called
 exactly `expected` number of times when the test is complete, then the test will
 fail.
 
-If `fn` is not provided, `common.noop` will be used.
+If `fn` is not provided, an empty function will be used.
 
 ### mustCallAtLeast([fn][, minimum])
-* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) default = `common.noop`
+* `fn` [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) default = () => {}
 * `minimum` [<Number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) default = 1
 * return [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
 
 Returns a function that calls `fn`. If the returned function has not been called
 at least `minimum` number of times when the test is complete, then the test will
 fail.
 
-If `fn` is not provided, `common.noop` will be used.
+If `fn` is not provided, an empty function will be used.
 
 ### mustNotCall([msg])
 * `msg` [<String>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type) default = 'function should not have been called'
@@ -217,19 +217,6 @@ Returns a function that triggers an `AssertionError` if it is invoked. `msg` is
 
 Returns `true` if the exit code `exitCode` and/or signal name `signal` represent the exit code and/or signal name of a node process that aborted, `false` otherwise.
 
-### noop
-
-A non-op `Function` that can be used for a variety of scenarios.
-
-For instance,
-
-<!-- eslint-disable strict, no-undef -->
-```js
-const common = require('../common');
-
-someAsyncAPI('foo', common.mustCall(common.noop));
-```
-
 ### opensslCli
 * return [&lt;Boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
 

Diff for: test/common/index.js

@@ -14,7 +14,6 @@ const testRoot = process.env.NODE_TEST_DIR ?
 
 const noop = () => {};
 
-exports.noop = noop;
 exports.fixturesDir = path.join(__dirname, '..', 'fixtures');
 exports.tmpDirName = 'tmp';
 // PORT should match the definition in test/testpy/__init__.py.

Diff for: test/debugger/test-debugger-client.js

@@ -129,7 +129,7 @@ addTest(function(client, done) {
 
 let connectCount = 0;
 const script = 'setTimeout(function() { console.log("blah"); });' +
-               'setInterval(common.noop, 1000000);';
+               'setInterval(() => {}, 1000000);';
 
 let nodeProcess;
 
@@ -172,7 +172,7 @@ function doTest(cb, done) {
         console.error('>>> connecting...');
         c.connect(debug.port);
         c.on('break', function() {
-          c.reqContinue(common.noop);
+          c.reqContinue(() => {});
         });
         c.on('ready', function() {
           connectCount++;

Diff for: test/parallel/test-assert.js

@@ -1,5 +1,5 @@
 'use strict';
-const common = require('../common');
+require('../common');
 const assert = require('assert');
 const a = require('assert');
 
@@ -515,7 +515,7 @@ testAssertionMessage(/a/, '/a/');
 testAssertionMessage(/abc/gim, '/abc/gim');
 testAssertionMessage(function f() {}, '[Function: f]');
 testAssertionMessage(function() {}, '[Function]');
-testAssertionMessage(common.noop, '[Function: noop]');
+testAssertionMessage(() => {}, '[Function]');
 testAssertionMessage({}, '{}');
 testAssertionMessage(circular, '{ y: 1, x: [Circular] }');
 testAssertionMessage({a: undefined, b: null}, '{ a: undefined, b: null }');

Diff for: test/parallel/test-cluster-rr-domain-listen.js

@@ -8,10 +8,10 @@ const domain = require('domain');
 
 if (cluster.isWorker) {
   const d = domain.create();
-  d.run(function() { });
+  d.run(() => {});
 
   const http = require('http');
-  http.Server(function() { }).listen(0, '127.0.0.1');
+  http.Server(() => {}).listen(0, '127.0.0.1');
 
 } else if (cluster.isMaster) {
   let worker;

Diff for: test/parallel/test-cluster-worker-wait-server-close.js

@@ -11,7 +11,7 @@ if (cluster.isWorker) {
   const server = net.createServer(function(socket) {
     // Wait for any data, then close connection
     socket.write('.');
-    socket.on('data', function discard() {});
+    socket.on('data', () => {});
   }).listen(0, common.localhostIPv4);
 
   server.once('close', function() {
@@ -20,7 +20,7 @@ if (cluster.isWorker) {
 
   // Although not typical, the worker process can exit before the disconnect
   // event fires. Use this to keep the process open until the event has fired.
-  const keepOpen = setInterval(common.noop, 9999);
+  const keepOpen = setInterval(() => {}, 9999);
 
   // Check worker events and properties
   process.once('disconnect', function() {

Diff for: test/parallel/test-common.js

@@ -10,11 +10,11 @@ global.gc = 42;  // Not a valid global unless --expose_gc is set.
 assert.deepStrictEqual(common.leakedGlobals(), ['gc']);
 
 assert.throws(function() {
-  common.mustCall(common.noop, 'foo');
+  common.mustCall(() => {}, 'foo');
 }, /^TypeError: Invalid exact value: foo$/);
 
 assert.throws(function() {
-  common.mustCall(common.noop, /foo/);
+  common.mustCall(() => {}, /foo/);
 }, /^TypeError: Invalid exact value: \/foo\/$/);
 
 const fnOnce = common.mustCall(() => {});

Diff for: test/parallel/test-crypto-random.js

@@ -16,7 +16,7 @@ const expectedErrorRegexp = /^TypeError: size must be a number >= 0$/;
 [crypto.randomBytes, crypto.pseudoRandomBytes].forEach(function(f) {
   [-1, undefined, null, false, true, {}, []].forEach(function(value) {
     assert.throws(function() { f(value); }, expectedErrorRegexp);
-    assert.throws(function() { f(value, common.noop); }, expectedErrorRegexp);
+    assert.throws(function() { f(value, () => {}); }, expectedErrorRegexp);
   });
 
   [0, 1, 2, 4, 16, 256, 1024].forEach(function(len) {

Diff for: test/parallel/test-env-var-no-warnings.js

@@ -29,7 +29,7 @@ if (process.argv[2] === 'child') {
   test({ NODE_NO_WARNINGS: false });
   test({ NODE_NO_WARNINGS: {} });
   test({ NODE_NO_WARNINGS: [] });
-  test({ NODE_NO_WARNINGS: common.noop });
+  test({ NODE_NO_WARNINGS: () => {} });
   test({ NODE_NO_WARNINGS: 0 });
   test({ NODE_NO_WARNINGS: -1 });
   test({ NODE_NO_WARNINGS: '0' });

Diff for: test/parallel/test-event-emitter-check-listener-leaks.js

@@ -1,46 +1,46 @@
 'use strict';
-const common = require('../common');
+require('../common');
 const assert = require('assert');
 const events = require('events');
 
 let e = new events.EventEmitter();
 
 // default
 for (let i = 0; i < 10; i++) {
-  e.on('default', common.noop);
+  e.on('default', () => {});
 }
 assert.ok(!e._events['default'].hasOwnProperty('warned'));
-e.on('default', common.noop);
+e.on('default', () => {});
 assert.ok(e._events['default'].warned);
 
 // symbol
 const symbol = Symbol('symbol');
 e.setMaxListeners(1);
-e.on(symbol, common.noop);
+e.on(symbol, () => {});
 assert.ok(!e._events[symbol].hasOwnProperty('warned'));
-e.on(symbol, common.noop);
+e.on(symbol, () => {});
 assert.ok(e._events[symbol].hasOwnProperty('warned'));
 
 // specific
 e.setMaxListeners(5);
 for (let i = 0; i < 5; i++) {
-  e.on('specific', common.noop);
+  e.on('specific', () => {});
 }
 assert.ok(!e._events['specific'].hasOwnProperty('warned'));
-e.on('specific', common.noop);
+e.on('specific', () => {});
 assert.ok(e._events['specific'].warned);
 
 // only one
 e.setMaxListeners(1);
-e.on('only one', common.noop);
+e.on('only one', () => {});
 assert.ok(!e._events['only one'].hasOwnProperty('warned'));
-e.on('only one', common.noop);
+e.on('only one', () => {});
 assert.ok(e._events['only one'].hasOwnProperty('warned'));
 
 // unlimited
 e.setMaxListeners(0);
 for (let i = 0; i < 1000; i++) {
-  e.on('unlimited', common.noop);
+  e.on('unlimited', () => {});
 }
 assert.ok(!e._events['unlimited'].hasOwnProperty('warned'));
 
@@ -49,26 +49,26 @@ events.EventEmitter.defaultMaxListeners = 42;
 e = new events.EventEmitter();
 
 for (let i = 0; i < 42; ++i) {
-  e.on('fortytwo', common.noop);
+  e.on('fortytwo', () => {});
 }
 assert.ok(!e._events['fortytwo'].hasOwnProperty('warned'));
-e.on('fortytwo', common.noop);
+e.on('fortytwo', () => {});
 assert.ok(e._events['fortytwo'].hasOwnProperty('warned'));
 delete e._events['fortytwo'].warned;
 
 events.EventEmitter.defaultMaxListeners = 44;
-e.on('fortytwo', common.noop);
+e.on('fortytwo', () => {});
 assert.ok(!e._events['fortytwo'].hasOwnProperty('warned'));
-e.on('fortytwo', common.noop);
+e.on('fortytwo', () => {});
 assert.ok(e._events['fortytwo'].hasOwnProperty('warned'));
 
 // but _maxListeners still has precedence over defaultMaxListeners
 events.EventEmitter.defaultMaxListeners = 42;
 e = new events.EventEmitter();
 e.setMaxListeners(1);
-e.on('uno', common.noop);
+e.on('uno', () => {});
 assert.ok(!e._events['uno'].hasOwnProperty('warned'));
-e.on('uno', common.noop);
+e.on('uno', () => {});
 assert.ok(e._events['uno'].hasOwnProperty('warned'));
 
 // chainable

Diff for: test/parallel/test-event-emitter-get-max-listeners.js

@@ -1,5 +1,5 @@
 'use strict';
-const common = require('../common');
+require('../common');
 const assert = require('assert');
 const EventEmitter = require('events');
 
@@ -15,5 +15,5 @@ assert.strictEqual(emitter.getMaxListeners(), 3);
 
 // https://github.com/nodejs/node/issues/523 - second call should not throw.
 const recv = {};
-EventEmitter.prototype.on.call(recv, 'event', common.noop);
-EventEmitter.prototype.on.call(recv, 'event', common.noop);
+EventEmitter.prototype.on.call(recv, 'event', () => {});
+EventEmitter.prototype.on.call(recv, 'event', () => {});

Diff for: test/parallel/test-event-emitter-listener-count.js

@@ -1,15 +1,15 @@
 'use strict';
 
-const common = require('../common');
+require('../common');
 const assert = require('assert');
 const EventEmitter = require('events');
 
 const emitter = new EventEmitter();
-emitter.on('foo', common.noop);
-emitter.on('foo', common.noop);
-emitter.on('baz', common.noop);
+emitter.on('foo', () => {});
+emitter.on('foo', () => {});
+emitter.on('baz', () => {});
 // Allow any type
-emitter.on(123, common.noop);
+emitter.on(123, () => {});
 
 assert.strictEqual(EventEmitter.listenerCount(emitter, 'foo'), 2);
 assert.strictEqual(emitter.listenerCount('foo'), 2);

Diff for: test/parallel/test-event-emitter-max-listeners-warning-for-null.js

@@ -18,5 +18,5 @@ process.on('warning', common.mustCall((warning) => {
   assert.ok(warning.message.includes('2 null listeners added.'));
 }));
 
-e.on(null, common.noop);
-e.on(null, common.noop);
+e.on(null, () => {});
+e.on(null, () => {});

Diff for: test/parallel/test-event-emitter-max-listeners-warning-for-symbol.js

@@ -20,5 +20,5 @@ process.on('warning', common.mustCall((warning) => {
   assert.ok(warning.message.includes('2 Symbol(symbol) listeners added.'));
 }));
 
-e.on(symbol, common.noop);
-e.on(symbol, common.noop);
+e.on(symbol, () => {});
+e.on(symbol, () => {});

Diff for: test/parallel/test-event-emitter-max-listeners-warning.js

@@ -18,6 +18,6 @@ process.on('warning', common.mustCall((warning) => {
   assert.ok(warning.message.includes('2 event-type listeners added.'));
 }));
 
-e.on('event-type', common.noop);
-e.on('event-type', common.noop);  // Trigger warning.
-e.on('event-type', common.noop);  // Verify that warning is emitted only once.
+e.on('event-type', () => {});
+e.on('event-type', () => {});  // Trigger warning.
+e.on('event-type', () => {});  // Verify that warning is emitted only once.

Diff for: test/parallel/test-event-emitter-remove-all-listeners.js

@@ -70,9 +70,9 @@ function listener() {}
   ee.on('removeListener', function(name, listener) {
     assert.strictEqual(expectLength--, this.listeners('baz').length);
   });
-  ee.on('baz', common.noop);
-  ee.on('baz', common.noop);
-  ee.on('baz', common.noop);
+  ee.on('baz', () => {});
+  ee.on('baz', () => {});
+  ee.on('baz', () => {});
   assert.strictEqual(ee.listeners('baz').length, expectLength + 1);
   ee.removeAllListeners('baz');
   assert.strictEqual(ee.listeners('baz').length, 0);

Diff for: test/parallel/test-event-emitter-subclass.js

@@ -41,6 +41,6 @@ MyEE2.prototype = new EventEmitter();
 const ee1 = new MyEE2();
 const ee2 = new MyEE2();
 
-ee1.on('x', common.noop);
+ee1.on('x', () => {});
 
 assert.strictEqual(ee2.listenerCount('x'), 0);

Diff for: test/parallel/test-fs-buffertype-writesync.js

@@ -9,7 +9,7 @@ const fs = require('fs');
 const path = require('path');
 
 const filePath = path.join(common.tmpDir, 'test_buffer_type');
-const v = [true, false, 0, 1, Infinity, common.noop, {}, [], undefined, null];
+const v = [true, false, 0, 1, Infinity, () => {}, {}, [], undefined, null];
 
 common.refreshTmpDir();
 

Diff for: test/parallel/test-fs-mkdir.js

@@ -56,4 +56,4 @@ common.refreshTmpDir();
 
 // Keep the event loop alive so the async mkdir() requests
 // have a chance to run (since they don't ref the event loop).
-process.nextTick(common.noop);
+process.nextTick(() => {});

Diff for: test/parallel/test-fs-read-stream-inherit.js

@@ -139,7 +139,7 @@ let paused = false;
   let file7 =
     fs.createReadStream(rangeFile, Object.create({autoClose: false }));
   assert.strictEqual(file7.autoClose, false);
-  file7.on('data', common.noop);
+  file7.on('data', () => {});
   file7.on('end', common.mustCall(function() {
     process.nextTick(common.mustCall(function() {
       assert(!file7.closed);
@@ -169,7 +169,7 @@ let paused = false;
 {
   const options = Object.create({fd: 13337, autoClose: false});
   const file8 = fs.createReadStream(null, options);
-  file8.on('data', common.noop);
+  file8.on('data', () => {});
   file8.on('error', common.mustCall());
   process.on('exit', function() {
     assert(!file8.closed);
@@ -181,7 +181,7 @@ let paused = false;
 // Make sure stream is destroyed when file does not exist.
 {
   const file9 = fs.createReadStream('/path/to/file/that/does/not/exist');
-  file9.on('data', common.noop);
+  file9.on('data', () => {});
   file9.on('error', common.mustCall());
 
   process.on('exit', function() {

Diff for: test/parallel/test-fs-read-stream.js

@@ -138,7 +138,7 @@ pauseRes.pause();
 pauseRes.resume();
 
 let file7 = fs.createReadStream(rangeFile, {autoClose: false });
-file7.on('data', common.noop);
+file7.on('data', () => {});
 file7.on('end', function() {
   process.nextTick(function() {
     assert(!file7.closed);
@@ -161,12 +161,12 @@ function file7Next() {
 
 // Just to make sure autoClose won't close the stream because of error.
 const file8 = fs.createReadStream(null, {fd: 13337, autoClose: false });
-file8.on('data', common.noop);
+file8.on('data', () => {});
 file8.on('error', common.mustCall());
 
 // Make sure stream is destroyed when file does not exist.
 const file9 = fs.createReadStream('/path/to/file/that/does/not/exist');
-file9.on('data', common.noop);
+file9.on('data', () => {});
 file9.on('error', common.mustCall());
 
 process.on('exit', function() {