Make Test_Widget compatible with WP_Widget (#34355)

* Make Test_Widget compatible with WP_Widget

* Move the isset($instance['title']) from update() to form() where it's needed

* Explain why codingStandardsIgnoreStart

packages/e2e-tests/plugins/class-test-widget.php

@@ -48,7 +48,7 @@ public function form( $instance ) {
 		?>
 		<p>
 			<label for="<?php echo $this->get_field_id( 'title' ); ?>">Title:</label>
-			<input class="widefat" id="<?php echo $this->get_field_id( 'title' ); ?>" name="<?php echo $this->get_field_name( 'title' ); ?>" type="text" value="<?php echo esc_attr( $instance['title'] ); ?>" />
+			<input class="widefat" id="<?php echo $this->get_field_id( 'title' ); ?>" name="<?php echo $this->get_field_name( 'title' ); ?>" type="text" value="<?php echo esc_attr( isset( $instance['title'] ) ? $instance['title'] : '' ); ?>" />
 		</p>
 		<?php
 	}
@@ -58,11 +58,14 @@ public function form( $instance ) {
 	 *
 	 * @param array $new_instance New settings for this instance as input by the user via
 	 *                            WP_Widget::form().
+	 * @param array $old_instance Old settings for this instance.
 	 *
 	 * @return array Settings to save or bool false to cancel saving.
 	 * @since 4.8.1
 	 */
-	public function update( $new_instance ) {
+	// @codingStandardsIgnoreStart – to prevent phpcs from complaining about unused function argument.
+	public function update( $new_instance, $old_instance ) {
+	// @codingStandardsIgnoreEnd
 		$instance          = array();
 		$instance['title'] = ( ! empty( $new_instance['title'] ) ) ? strip_tags( $new_instance['title'] ) : '';
 		return $instance;