Return early if core cache functions are already defined, usefull for PHPUnit tests for instance.

Author: Hug0-Drelon

drop-in.php

@@ -556,6 +556,10 @@ private function get_cache_file_path( $key, $group ) {
 /**
  * Core cache functions implementation.
  */
+if ( function_exists( 'wp_cache_init' ) ) {
+	// Should not happen except in PHPUnit tests.
+	return;
+}
 
 // phpcs:disable NeutronStandard.Globals.DisallowGlobalFunctions.GlobalFunctions
 // phpcs:disable Squiz.Commenting.FunctionComment.Missing