Add MockMessageLocalizer

This MessageLocalizer may be used in tests. By default, it sets the
language for all messages to 'qqx', to make the tests independent of the
$wgLanguageCode of the wiki the tests are running in.

Change-Id: I7412ec49b6c0fab8146e09bb8aa599b35d88fc97

tests/phpunit/mocks/MockMessageLocalizer.php

@@ -0,0 +1,53 @@
+<?php
+
+use Message;
+use MessageLocalizer;
+use MessageSpecifier;
+
+/**
+ * A simple {@link MessageLocalizer} implementation for use in tests.
+ * By default, it sets the message language to 'qqx',
+ * to make the tests independent of the wiki configuration.
+ *
+ * @author Lucas Werkmeister
+ * @license GPL-2.0-or-later
+ */
+class MockMessageLocalizer implements MessageLocalizer {
+
+	/**
+	 * @var string|null
+	 */
+	private $languageCode;
+
+	/**
+	 * @param string|null $languageCode The language code to use for messages by default.
+	 * You can specify null to use the user language,
+	 * but this is not recommended as it may make your tests depend on the wiki configuration.
+	 */
+	public function __construct( $languageCode = 'qqx' ) {
+		$this->languageCode = $languageCode;
+	}
+
+	/**
+	 * Get a Message object.
+	 * Parameters are the same as {@link wfMessage()}.
+	 *
+	 * @param string|string[]|MessageSpecifier $key Message key, or array of keys,
+	 *   or a MessageSpecifier.
+	 * @param mixed $args,...
+	 * @return Message
+	 */
+	public function msg( $key ) {
+		$args = func_get_args();
+
+		/** @var Message $message */
+		$message = call_user_func_array( 'wfMessage', $args );
+
+		if ( $this->languageCode !== null ) {
+			$message->inLanguage( $this->languageCode );
+		}
+
+		return $message;
+	}
+
+}