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>

test/common/README.md

@@ -209,26 +209,26 @@ 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'
@@ -243,19 +243,6 @@ 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)
 

test/common/index.js

@@ -37,7 +37,6 @@ 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.

test/message/unhandled_promise_trace_warnings.js

@@ -1,5 +1,5 @@
 // Flags: --trace-warnings
 'use strict';
-const common = require('../common');
+require('../common');
 const p = Promise.reject(new Error('This was rejected'));
-setImmediate(() => p.catch(common.noop));
+setImmediate(() => p.catch(() => {}));

test/parallel/test-assert.js

@@ -571,29 +571,30 @@ a.throws(makeBlock(a.deepEqual, args, []));
 
 // check messages from assert.throws()
 {
+  const noop = () => {};
   assert.throws(
-    () => { a.throws(common.noop); },
+    () => { a.throws((noop)); },
     common.expectsError({
       code: 'ERR_ASSERTION',
       message: /^Missing expected exception\.$/
     }));
 
   assert.throws(
-    () => { a.throws(common.noop, TypeError); },
+    () => { a.throws(noop, TypeError); },
     common.expectsError({
       code: 'ERR_ASSERTION',
       message: /^Missing expected exception \(TypeError\)\.$/
     }));
 
   assert.throws(
-    () => { a.throws(common.noop, 'fhqwhgads'); },
+    () => { a.throws(noop, 'fhqwhgads'); },
     common.expectsError({
       code: 'ERR_ASSERTION',
       message: /^Missing expected exception: fhqwhgads$/
     }));
 
   assert.throws(
-    () => { a.throws(common.noop, TypeError, 'fhqwhgads'); },
+    () => { a.throws(noop, TypeError, 'fhqwhgads'); },
     common.expectsError({
       code: 'ERR_ASSERTION',
       message: /^Missing expected exception \(TypeError\): fhqwhgads$/

test/parallel/test-buffer-includes.js

@@ -1,5 +1,5 @@
 'use strict';
-const common = require('../common');
+require('../common');
 const assert = require('assert');
 
 const b = Buffer.from('abcdef');
@@ -274,7 +274,7 @@ for (let lengthIndex = 0; lengthIndex < lengths.length; lengthIndex++) {
 const expectedError =
   /^TypeError: "val" argument must be string, number, Buffer or Uint8Array$/;
 assert.throws(() => {
-  b.includes(common.noop);
+  b.includes(() => {});
 }, expectedError);
 assert.throws(() => {
   b.includes({});

test/parallel/test-child-process-bad-stdio.js

@@ -5,7 +5,7 @@ const assert = require('assert');
 const cp = require('child_process');
 
 if (process.argv[2] === 'child') {
-  setTimeout(common.noop, common.platformTimeout(100));
+  setTimeout(() => {}, common.platformTimeout(100));
   return;
 }
 

test/parallel/test-child-process-spawnsync-kill-signal.js

@@ -4,7 +4,7 @@ const assert = require('assert');
 const cp = require('child_process');
 
 if (process.argv[2] === 'child') {
-  setInterval(common.noop, 1000);
+  setInterval(() => {}, 1000);
 } else {
   const { SIGKILL } = process.binding('constants').os.signals;
 

test/parallel/test-cluster-rr-domain-listen.js

@@ -20,7 +20,7 @@
 // USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 'use strict';
-const common = require('../common');
+require('../common');
 const cluster = require('cluster');
 const domain = require('domain');
 
@@ -29,10 +29,10 @@ const domain = require('domain');
 
 if (cluster.isWorker) {
   const d = domain.create();
-  d.run(common.noop);
+  d.run(() => {});
 
   const http = require('http');
-  http.Server(common.noop).listen(0, '127.0.0.1');
+  http.Server(() => {}).listen(0, '127.0.0.1');
 
 } else if (cluster.isMaster) {
 

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', common.noop);
+    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() {

test/parallel/test-common.js

@@ -101,7 +101,7 @@ const HIJACK_TEST_ARRAY = [ 'foo\n', 'bar\n', 'baz\n' ];
   assert.notStrictEqual(originalWrite, stream.write);
 
   HIJACK_TEST_ARRAY.forEach((val) => {
-    stream.write(val, common.mustCall(common.noop));
+    stream.write(val, common.mustCall());
   });
 
   assert.strictEqual(HIJACK_TEST_ARRAY.length, stream.writeTimes);

test/parallel/test-console-instance.js

@@ -43,7 +43,7 @@ assert.throws(() => {
 
 // Console constructor should throw if stderr exists but is not writable
 assert.throws(() => {
-  out.write = common.noop;
+  out.write = () => {};
   err.write = undefined;
   new Console(out, err);
 }, /^TypeError: Console expects writable stream instances$/);

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', () => {});

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);

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, () => {});

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, () => {});

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.

test/parallel/test-event-emitter-remove-listeners.js

@@ -140,7 +140,7 @@ function listener2() {}
 {
   const ee = new EventEmitter();
 
-  assert.deepStrictEqual(ee, ee.removeListener('foo', common.noop));
+  assert.deepStrictEqual(ee, ee.removeListener('foo', () => {}));
 }
 
 // Verify that the removed listener must be a function
@@ -152,7 +152,7 @@ assert.throws(() => {
 
 {
   const ee = new EventEmitter();
-  const listener = common.noop;
+  const listener = () => {};
   ee._events = undefined;
   const e = ee.removeListener('foo', listener);
   assert.strictEqual(e, ee);

test/parallel/test-event-emitter-special-event-names.js

@@ -5,7 +5,7 @@ const EventEmitter = require('events');
 const assert = require('assert');
 
 const ee = new EventEmitter();
-const handler = common.noop;
+const handler = () => {};
 
 assert.deepStrictEqual(ee.eventNames(), []);
 

test/parallel/test-event-emitter-subclass.js

@@ -62,6 +62,6 @@ 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);

test/parallel/test-events-list.js

@@ -5,7 +5,6 @@ const EventEmitter = require('events');
 const assert = require('assert');
 
 const EE = new EventEmitter();
-// Do not use common.noop here, these need to be separate listener functions
 const m = () => {};
 EE.on('foo', () => {});
 assert.deepStrictEqual(['foo'], EE.eventNames());

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();
 

test/parallel/test-fs-mkdir.js

@@ -77,4 +77,4 @@ 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(() => {});

test/parallel/test-handle-wrap-isrefed.js

@@ -87,7 +87,7 @@ const strictEqual = require('assert').strictEqual;
 // tcp
 {
   const net = require('net');
-  const server = net.createServer(common.noop).listen(0);
+  const server = net.createServer(() => {}).listen(0);
   strictEqual(Object.getPrototypeOf(server._handle).hasOwnProperty('hasRef'),
               true, 'tcp_wrap: hasRef() missing');
   strictEqual(server._handle.hasRef(),
@@ -112,7 +112,7 @@ const strictEqual = require('assert').strictEqual;
 
 // timers
 {
-  const timer = setTimeout(common.noop, 500);
+  const timer = setTimeout(() => {}, 500);
   timer.unref();
   strictEqual(Object.getPrototypeOf(timer._handle).hasOwnProperty('hasRef'),
               true, 'timer_wrap: hasRef() missing');

test/parallel/test-http-client-defaults.js

@@ -1,23 +1,23 @@
 'use strict';
 
-const common = require('../common');
+require('../common');
 const assert = require('assert');
 const ClientRequest = require('http').ClientRequest;
 
 {
-  const req = new ClientRequest({ createConnection: common.noop });
+  const req = new ClientRequest({ createConnection: () => {} });
   assert.strictEqual(req.path, '/');
   assert.strictEqual(req.method, 'GET');
 }
 
 {
-  const req = new ClientRequest({ method: '', createConnection: common.noop });
+  const req = new ClientRequest({ method: '', createConnection: () => {} });
   assert.strictEqual(req.path, '/');
   assert.strictEqual(req.method, 'GET');
 }
 
 {
-  const req = new ClientRequest({ path: '', createConnection: common.noop });
+  const req = new ClientRequest({ path: '', createConnection: () => {} });
   assert.strictEqual(req.path, '/');
   assert.strictEqual(req.method, 'GET');
 }

test/parallel/test-http-parser-bad-ref.js

@@ -4,7 +4,7 @@
 
 // Flags: --expose_gc
 
-const common = require('../common');
+require('../common');
 const assert = require('assert');
 const HTTPParser = process.binding('http_parser').HTTPParser;
 
@@ -39,7 +39,7 @@ function demoBug(part1, part2) {
     console.log('url', info.url);
   };
 
-  parser[kOnBody] = common.noop;
+  parser[kOnBody] = () => {};
 
   parser[kOnMessageComplete] = function() {
     messagesComplete++;

test/parallel/test-http-upgrade-server.js

@@ -21,7 +21,7 @@
 
 'use strict';
 
-const common = require('../common');
+require('../common');
 const assert = require('assert');
 
 const util = require('util');
@@ -38,7 +38,7 @@ function createTestServer() {
 }
 
 function testServer() {
-  http.Server.call(this, common.noop);
+  http.Server.call(this, () => {});
 
   this.on('connection', function() {
     requests_recv++;