Handled missing DOM extension during XML import

includes/Importers/WP/WXR_Parser.php

@@ -63,7 +63,7 @@ public function parse( $file ) {
 		}
 
 		// Attempt to use proper XML parsers first
-		if ( extension_loaded( 'simplexml' ) ) {
+		if ( $this->can_use_simplexml() ) {
 			$parser = new WXR_Parser_SimpleXML();
 			$this->logger->log( 'Using WXR_Parser_SimpleXML...', 'progress' );
 			$result = $parser->parse( $file );
@@ -92,4 +92,13 @@ public function parse( $file ) {
 
 		return $result;
 	}
+
+	/**
+	 * Check whether the SimpleXML parser can run; it loads the file through DOMDocument.
+	 *
+	 * @return bool
+	 */
+	protected function can_use_simplexml() {
+		return extension_loaded( 'simplexml' ) && class_exists( 'DOMDocument' );
+	}
 }

tests/wxr-parser-test.php

@@ -0,0 +1,46 @@
+<?php
+/**
+ * WXR parser selection tests.
+ *
+ * @package templates-patterns-collection
+ */
+
+use TIOB\Importers\WP\WXR_Parser;
+use TIOB\Importers\WP\WXR_Parser_SimpleXML;
+use TIOB\Importers\WP\WXR_Parser_XML;
+
+/**
+ * WXR parser on a host without the DOM extension.
+ */
+class WXR_Parser_Without_Dom extends WXR_Parser {
+	protected function can_use_simplexml(): bool {
+		return false;
+	}
+}
+
+/**
+ * Class WXR_Parser_Test
+ */
+class WXR_Parser_Test extends WP_UnitTestCase {
+	/**
+	 * @var string
+	 */
+	private $file;
+
+	public function setUp(): void {
+		parent::setUp();
+		$this->file = __DIR__ . '/fixtures/export.xml';
+	}
+
+	public function test_parse_uses_simplexml_parser_when_dom_is_available(): void {
+		$expected = ( new WXR_Parser_SimpleXML() )->parse( $this->file );
+
+		$this->assertSame( $expected, ( new WXR_Parser( 'gutenberg' ) )->parse( $this->file ) );
+	}
+
+	public function test_parse_falls_back_to_xml_parser_when_dom_is_unavailable(): void {
+		$expected = ( new WXR_Parser_XML() )->parse( $this->file );
+
+		$this->assertSame( $expected, ( new WXR_Parser_Without_Dom( 'gutenberg' ) )->parse( $this->file ) );
+	}
+}