test: refactor test-fs-watchfile

* use `common.mustNotCall()` to confirm callback is not called
* reorder modules to conform with test-writing guide
* match full error message in `assert.throws()`

PR-URL: nodejs#13721
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-fs-watchfile.js

@@ -1,21 +1,21 @@
 'use strict';
-
 const common = require('../common');
+
+const assert = require('assert');
 const fs = require('fs');
 const path = require('path');
-const assert = require('assert');
 
 // Basic usage tests.
 assert.throws(function() {
   fs.watchFile('./some-file');
-}, /"watchFile\(\)" requires a listener function/);
+}, /^Error: "watchFile\(\)" requires a listener function$/);
 
 assert.throws(function() {
   fs.watchFile('./another-file', {}, 'bad listener');
-}, /"watchFile\(\)" requires a listener function/);
+}, /^Error: "watchFile\(\)" requires a listener function$/);
 
 assert.throws(function() {
-  fs.watchFile(new Object(), common.noop);
+  fs.watchFile(new Object(), common.mustNotCall());
 }, /Path must be a string/);
 
 const enoentFile = path.join(common.tmpDir, 'non-existent-file');