First working test.

extension.json

@@ -34,7 +34,8 @@
         },
         "AutoloadClasses": {
                 "LinkTitles\\Extension": "includes/LinkTitles_Extension.php",
-                "LinkTitles\\Special": "includes/LinkTitles_Special.php"
+                "LinkTitles\\Special": "includes/LinkTitles_Special.php",
+                "LinkTitles\\TestCase": "tests/phpunit/TestCase.php"
         },
         "SpecialPages": {
                 "LinkTitles": "LinkTitles\\Special"

includes/LinkTitles_Extension.php

@@ -73,6 +73,12 @@ class Extension {
 		self::BuildDelimiters();
 	}
 
+	/// Helper method to be used in unit testing, were everything takes place
+	/// in one request.
+	public static function invalidateCache() {
+		self::fetchPageTitles();
+	}
+
 	/// Event handler that is hooked to the PageContentSave event.
 	public static function onPageContentSave( &$wikiPage, &$user, &$content, &$summary,
 			$isMinor, $isWatch, $section, &$flags, &$status ) {
@@ -135,7 +141,7 @@ class Extension {
 
 		if ( !isset( self::$pageTitles ) || ( $currentNamespace != self::$currentNamespace ) ) {
 			self::$currentNamespace = $currentNamespace;
-			self::$pageTitles = self::fetchPageTitles( $currentNamespace );
+			self::fetchPageTitles();
 		}
 
 		// Iterate through the page titles
@@ -269,8 +275,7 @@ class Extension {
 	}
 
 	// Fetches the page titles from the database.
-	// @param $currentNamespace String holding the namespace of the page currently being processed.
-	private static function fetchPageTitles( $currentNamespace ) {
+	private static function fetchPageTitles() {
 		global $wgLinkTitlesPreferShortTitles;
 		global $wgLinkTitlesMinimumTitleLength;
 		global $wgLinkTitlesBlackList;
@@ -282,8 +287,8 @@ class Extension {
 		$blackList = str_replace( ' ', '_', '("' . implode( '","',$wgLinkTitlesBlackList ) . '")' );
 
 		// Build our weight list. Make sure current namespace is first element
-		$namespaces = array_diff( $wgLinkTitlesNamespaces, [ $currentNamespace ] );
-		array_unshift( $namespaces,  $currentNamespace );
+		$namespaces = array_diff( $wgLinkTitlesNamespaces, [ self::$currentNamespace ] );
+		array_unshift( $namespaces,  self::$currentNamespace );
 
 		// No need for sanitiy check. we are sure that we have at least one element in the array
 		$weightSelect = "CASE page_namespace ";
@@ -326,7 +331,8 @@ class Extension {
 			);
 		}
 
-		return $res;
+		self::$pageTitles = $res;
+		return true;
 	}
 
 	// Build an anonymous callback function to be used in simple mode.

tests/phpunit/ParseOnEditTest.php

@@ -0,0 +1,17 @@
+<?php
+/**
+ * @group bovender
+ * @group Database
+ */
+class ParseOnEditTest extends LinkTitles\TestCase {
+
+  public function testParseOnEdit() {
+    $this->setMwGlobals( [
+      'wgLinkTitlesParseOnEdit' => true,
+      'wgLinkTitlesParseOnRender' => true
+    ] );
+    $pageId = $this->insertPage( 'test page', 'This page should link to the link target' )['id'];
+    $page = WikiPage::newFromId( $pageId );
+    $this->assertSame( 'This page should link to the [[link target]]', self::getPageText( $page ) );
+  }
+}

tests/phpunit/TestCase.php

@@ -0,0 +1,19 @@
+<?php
+namespace LinkTitles;
+
+abstract class TestCase extends \MediaWikiTestCase {
+  protected function setUp() {
+    parent::setUp();
+    $this->insertPage( 'link target', 'This page serves as a link target' );
+    Extension::invalidateCache();
+  }
+
+  protected function tearDown() {
+    parent::tearDown();
+  }
+
+  protected function getPageText( \WikiPage $page ) {
+    $content = $page->getContent();
+    return $page->getContentHandler()->serializeContent( $content );
+  }
+}