Tests: Ensure that the default wp_die() handler can handle a WP_Error object.

Props dd32, utkarshpatel.
Fixes #36166.

git-svn-id: https://develop.svn.wordpress.org/trunk@37071 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/includes/testcase.php

@@ -292,6 +292,10 @@ class WP_UnitTestCase extends PHPUnit_Framework_TestCase {
 	}
 
 	function wp_die_handler( $message ) {
+		if ( ! is_scalar( $message ) ) {
+			$message = '0';
+		}
+
 		throw new WPDieException( $message );
 	}