doc: specify sorted requires in tests

And allow anchor links to the various sections, to more easily reference
them when reviewing PRs.

PR-URL: nodejs#10716
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>

doc/guides/writing-tests.md

@@ -29,8 +29,8 @@ Let's analyze this basic test from the Node.js test suite:
 4   // This test ensures that the http-parser can handle UTF-8 characters
 5   // in the http header.
 6
-7   const http = require('http');
-8   const assert = require('assert');
+7   const assert = require('assert');
+8   const http = require('http');
 9
 10  const server = http.createServer(common.mustCall((req, res) => {
 11    res.end('ok');
@@ -46,7 +46,7 @@ Let's analyze this basic test from the Node.js test suite:
 21 });
 ```
 
-**Lines 1-2**
+### **Lines 1-2**
 
 ```javascript
 'use strict';
@@ -70,7 +70,7 @@ assigning it to an identifier:
 require('../common');
 ```
 
-**Lines 4-5**
+### **Lines 4-5**
 
 ```javascript
 // This test ensures that the http-parser can handle UTF-8 characters
@@ -80,11 +80,11 @@ require('../common');
 A test should start with a comment containing a brief description of what it is
 designed to test.
 
-**Lines 7-8**
+### **Lines 7-8**
 
 ```javascript
-const http = require('http');
 const assert = require('assert');
+const http = require('http');
 ```
 
 The test checks functionality in the `http` module.
@@ -95,7 +95,7 @@ The require statements are sorted in
 [ASCII](http://man7.org/linux/man-pages/man7/ascii.7.html) order (digits, upper
 case, `_`, lower case).
 
-**Lines 10-21**
+### **Lines 10-21**
 
 This is the body of the test. This test is simple, it just tests that an
 HTTP server accepts `non-ASCII` characters in the headers of an incoming