[PhpUnitBridge] Fix enum_exists mock tests

Author: alexandre-daubois

Tests/EnumExistsMockTest.php

@@ -23,6 +23,9 @@ class EnumExistsMockTest extends TestCase
 {
     public static function setUpBeforeClass(): void
     {
+        // Require the fixture file to allow PHP to be fully aware of the enum existence
+        require __DIR__.'/Fixtures/ExistingEnumReal.php';
+
         ClassExistsMock::register(__CLASS__);
     }
 
@@ -34,6 +37,11 @@ protected function setUp(): void
         ]);
     }
 
+    public static function tearDownAfterClass(): void
+    {
+        ClassExistsMock::withMockedEnums([]);
+    }
+
     public function testClassExists()
     {
         $this->assertFalse(class_exists(ExistingEnum::class));