Because the title was emptied, the post update failed entirely, leaving the original content.

Author: dmsnell

tests/phpunit/tests/post/wpPublishPost.php

@@ -88,7 +88,7 @@ public function test_wp_update_post_with_content_filtering() {
 
 		$post_id = wp_insert_post(
 			array(
-				'post_title' => '<script>Test</script>',
+				'post_title' => 'Talking about: <script>Test</script>',
 			)
 		);
 		$post    = get_post( $post_id );
@@ -107,7 +107,7 @@ public function test_wp_update_post_with_content_filtering() {
 		kses_remove_filters();
 
 		$post = get_post( $post->ID );
-		$this->assertSame( 'Test', $post->post_title );
+		$this->assertSame( 'Talking about: ', $post->post_title );
 	}
 
 	/**