Comments: Update comment cache in the upgrade routine for changing the comment_type DB field value in comments table.

This ensures that comment object cache is cleared after changing the comment type to `comment` instead of an empty string.

Add a unit test for `_wp_batch_update_comment_type()`.

Follow-up to [47597], [47626], [48225], [48227].

Props imath, westonruter.
Fixes #49236.

git-svn-id: https://develop.svn.wordpress.org/trunk@48748 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/comment/wpBatchUpdateCommentType.php

@@ -0,0 +1,49 @@
+<?php
+
+/**
+ * @group comment
+ * @covers ::_wp_batch_update_comment_type
+ */
+class Tests_Batch_Update_Comment_Type extends WP_UnitTestCase {
+
+	/**
+	 * @ticket 49236
+	 */
+	public function test__wp_batch_update_comment_type() {
+		global $wpdb;
+
+		$comment_ids     = self::factory()->comment->create_many( 3 );
+		$comment_id_list = implode( ',', $comment_ids );
+
+		$wpdb->query(
+			"UPDATE {$wpdb->comments}
+			SET comment_type = ''
+			WHERE comment_type = 'comment'
+			AND comment_ID in ({$comment_id_list})" // phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared
+		);
+
+		clean_comment_cache( $comment_ids );
+
+		foreach ( $comment_ids as $comment_id ) {
+			$comment = get_comment( $comment_id );
+			$this->assertEmpty( $comment->comment_type );
+		}
+
+		add_filter( 'wp_update_comment_type_batch_size', array( $this, 'filter_comment_type_batch_size' ) );
+		add_filter( 'schedule_event', '__return_null' );
+
+		_wp_batch_update_comment_type();
+
+		remove_filter( 'wp_update_comment_type_batch_size', array( $this, 'filter_comment_type_batch_size' ) );
+		remove_filter( 'schedule_event', '__return_null' );
+
+		foreach ( $comment_ids as $comment_id ) {
+			$updated_comment = get_comment( $comment_id );
+			$this->assertEquals( 'comment', $updated_comment->comment_type );
+		}
+	}
+
+	public function filter_comment_type_batch_size() {
+		return 3;
+	}
+}