Add more PRE tests

Author: sirreal

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

@@ -346,6 +346,14 @@ public static function data_provider_normalize_special_leading_newline_cases() {
 				"<pre>\n\nline 2\nline 3</pre>",
 				"<pre>\n\nline 2\nline 3</pre>",
 			),
+			'Multiple text nodes inside PRE' => array(
+				"<pre>\nline 1<!--comment--> still line 1</pre>",
+				"<pre>line 1<!--comment--> still line 1</pre>",
+			),
+			'Multiple text nodes inside PRE with leading newlines' => array(
+				"<pre>\n\nline 2<!--comment--> still line 2</pre>",
+				"<pre>\n\nline 2<!--comment--> still line 2</pre>",
+			),
 			'Leading newline in TEXTAREA' => array(
 				"<textarea>\nline 1\nline 2</textarea>",
 				"<textarea>line 1\nline 2</textarea>",