test: add common.noop, default for common.mustCall()

Export a new common.noop no-operation function for general use.
Allow using common.mustCall() without a fn argument to simplify
test cases.

Replace various non-op functions throughout tests with common.noop

PR-URL: #12027
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Teddy Katz <teddy.katz@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>

Author: jasnell

test/README.md

@@ -324,7 +324,7 @@ Gets IP of localhost
 
 Array of IPV6 hosts.
 
-### mustCall(fn[, expected])
+### mustCall([fn][, expected])
 * fn [<Function>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)
 * expected [<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)
@@ -333,13 +333,27 @@ 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.
+
 ### nodeProcessAborted(exitCode, signal)
 * `exitCode` [<Number>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type)
 * `signal` [<String>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type)
 * return [<Boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
 
 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,
+
+```js
+const common = require('../common');
+
+someAsyncAPI('foo', common.mustCall(common.noop));
+```
+
 ### opensslCli
 * return [<Boolean>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type)
 

test/addons/async-hello-world/test.js

@@ -6,5 +6,5 @@ const binding = require(`./build/${common.buildType}/binding`);
 binding(5, common.mustCall(function(err, val) {
   assert.strictEqual(err, null);
   assert.strictEqual(val, 10);
-  process.nextTick(common.mustCall(function() {}));
+  process.nextTick(common.mustCall());
 }));