Add a test to ensure the return variable prior to the end observer executing

Author: segrax

ext/zend_test/tests/observer_retval_alter_01.phpt

@@ -0,0 +1,34 @@
+--TEST--
+Observer: Retvals are modifiable by observers
+--EXTENSIONS--
+zend_test
+--INI--
+zend_test.observer.enabled=1
+zend_test.observer.show_output=1
+zend_test.observer.show_return_value=1
+zend_test.observer.observe_function_names=foo
+zend_test.observer.observe_end_call_function_name=hook
+--FILE--
+<?php
+function foo(string $pin): string {
+
+    return 'original return value';
+}
+
+function hook(): string {
+  return 'hook value';
+}
+
+$res = foo('some value'); // Retval used
+var_dump($res);
+echo 'Done' . PHP_EOL;
+?>
+--EXPECTF--
+<!-- init '%s/observer_retval_alter_%d.php' -->
+<!-- init foo() -->
+<foo>
+  <!-- init hook() -->
+</foo:'original return value'>
+<!-- init var_dump() -->
+string(10) "hook value"
+Done