Prevent test failure from E_USER_WARNING

Author: dmsnell

tests/phpunit/tests/html-api/wpHtmlProcessor-serialize.php

@@ -352,6 +352,13 @@ public function test_normalize_special_leading_newline_handling( string $input,
 	 */
 	public function test_normalize_fuzzer_cases_do_not_emit_native_errors( string $input, ?string $expected ) {
 		$errors = array();
+
+		/*
+		 * This test is checking for native PHP warnings/notices. Unsupported HTML may
+		 * intentionally cause wp_trigger_error() under WP_DEBUG, which is separate
+		 * from the native errors this regression test is trying to catch.
+		 */
+		add_filter( 'wp_trigger_error_trigger_error', '__return_false' );
 		set_error_handler(
 			static function ( int $errno, string $errstr ) use ( &$errors ) {
 				$errors[] = "{$errno}: {$errstr}";
@@ -363,6 +370,7 @@ static function ( int $errno, string $errstr ) use ( &$errors ) {
 			$normalized = WP_HTML_Processor::normalize( $input );
 		} finally {
 			restore_error_handler();
+			remove_filter( 'wp_trigger_error_trigger_error', '__return_false' );
 		}
 
 		// Use assertSame() instead of assertEmpty() so PHPUnit shows captured error messages on failure.