[URP][2023.2] Adding URPHelpURLAttribute tests

Adds editor tests for the `URPHelpURL `Attribute that is used to give documentation links in various places inside the editor.

These attributes were recently broken and undetected until package validation so this test was made to ensure that doesn't happen again.

Packages/com.unity.render-pipelines.universal/Tests/Editor/DocumentationTests.cs

@@ -0,0 +1,90 @@
+using System;
+using System.Collections.Generic;
+using System.Net;
+using System.Text;
+using NUnit.Framework;
+using UnityEditor;
+using UnityEngine;
+using UnityEngine.Rendering.Universal;
+
+namespace Documentation
+{
+    class DocumentationTests
+    {
+        private bool TestURL(string url)
+        {
+            try
+            {
+                HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
+
+                // Timeout set to 10 seconds
+                request.Timeout = 10000;
+
+                // Only get header information
+                request.Method = "HEAD";
+
+                using (HttpWebResponse response = request.GetResponse() as HttpWebResponse)
+                {
+                    int statusCode = (int)response.StatusCode;
+
+                    // Successful requests
+                    if (statusCode >= 100 && statusCode < 400)
+                        return true;
+
+                    // Server Errors
+                    if (statusCode >= 500 && statusCode <= 510)
+                        return false;
+                }
+            }
+            catch
+            {
+                // ignored
+            }
+
+            return false;
+        }
+
+        [Test]
+        public void TestURPHelpURLAttributes()
+        {
+            // Start with checking a bad URL to make sure TestURL() works.
+            string badURL = "https://docs.unity3d.com/Packages/com.unity.render-pipelines.universal@16.0/manual/incorrect-url";
+            bool badURLResults = TestURL(badURL);
+            Assert.IsFalse(badURLResults, "TestURL() failed. A broken URL should have been detected.");
+
+            // Find everything that uses URPHelpURLAttribute
+            TypeCache.TypeCollection typesWithHelpUrls = TypeCache.GetTypesWithAttribute<URPHelpURLAttribute>();
+
+            // Check if all the URLs are valid.
+            bool allURLsAreValid = true;
+            StringBuilder failures = new ();
+            foreach (Type type in typesWithHelpUrls)
+            {
+                Debug.Log("Checking \"" + type.FullName + "\"");
+                object[] attributes = type.GetCustomAttributes(typeof(URPHelpURLAttribute), false);
+                for (int i = 0; i < attributes.Length; i++)
+                {
+                    URPHelpURLAttribute attribute = attributes[i] as URPHelpURLAttribute;
+                    Assert.IsNotNull(attribute);
+
+                    string url = attribute.URL;
+                    bool urlIsValid = TestURL(url);
+
+                    Debug.Log("\t" + url);
+                    Debug.Log(urlIsValid ? "\tSuccess!\n" : "\tFailure!\n");
+
+                    if (urlIsValid)
+                        continue;
+
+                    allURLsAreValid = false;
+                    failures.AppendLine("\t" + type.FullName);
+                    failures.AppendLine("\t" + url);
+                    failures.AppendLine();
+                }
+            }
+
+            if (!allURLsAreValid)
+                Assert.Fail("The following URLs failed:\n" + failures);
+        }
+    }
+}