Defining the temp directory based on what the OS defines it as

tests/bootstrap.php

@@ -2,12 +2,14 @@
 
 declare(strict_types = 1);
 
+$tmp_dir = sys_get_temp_dir();
+
 // As WordPress is still using and supporting PHPUnit 6, we need to create
 // certain empty classes expected for that version of PHPUnit in order to
 // supress errors when we run PHPUnit 9.
 require __DIR__ . '/_/SupressFrameworkError.php';
 require __DIR__ . '/_/SupressFramework.php';
 
 // Include the WordPress test suite.
-require '/tmp/wordpress-tests-lib/includes/functions.php';
-require '/tmp/wordpress-tests-lib/includes/bootstrap.php';
+require "{$tmp_dir}/wordpress-tests-lib/includes/functions.php";
+require "{$tmp_dir}/wordpress-tests-lib/includes/bootstrap.php";