Added dummy enum declaration to conditionally include in test.

tests/AssertTest.php

@@ -836,10 +836,14 @@ public function testResourceOfTypeCustomMessage(): void
 
     public function testEnumAssertionErrorMessage(): void
     {
-        if (PHP_VERSION_ID < ENUM_INTRODUCTION_VERSION_ID) {
-            $this->markTestSkipped(sprintf('This test requires php %s or upper.', ENUM_INTRODUCTION_VERSION_ID));
+        $enumIntroductionVersion = 80100;
+
+        if (PHP_VERSION_ID < $enumIntroductionVersion) {
+            $this->markTestSkipped(sprintf('This test requires php %s or upper.', $enumIntroductionVersion));
         }
 
+        require_once 'DummyEnum.php';
+
         $this->expectException('\InvalidArgumentException');
         $this->expectExceptionMessage('Expected null. Got: Webmozart\Assert\Tests\TestEnum::CaseName');
 
@@ -867,12 +871,3 @@ public function __toString()
         return $this->value;
     }
 }
-
-const ENUM_INTRODUCTION_VERSION_ID = 80100;
-
-if (PHP_VERSION_ID >= ENUM_INTRODUCTION_VERSION_ID) {
-    enum TestEnum
-    {
-        case CaseName;
-    }
-}

tests/DummyEnum.php

@@ -0,0 +1,9 @@
+<?php
+
+namespace Webmozart\Assert\Tests;
+
+// The filename must be different from the class name to be ignored by composer PSR-4 autoloading rules
+enum TestEnum
+{
+    case CaseName;
+}