Improve error message if an abstract class is mocked in PHPUnit 12

src/Stub.php

@@ -462,6 +462,10 @@ private static function doGenerateMock($args, $isAbstract = false)
             $methodName = $isAbstract ? 'getMockForAbstractClass' : 'getMock';
         }
 
+        if ($isAbstract && version_compare(PHPUnitVersion::series(), '12', '>=')) {
+            throw new RuntimeException('PHPUnit 12 or greater does not allow to mock abstract classes anymore');
+        }
+
         // PHPUnit 10.3 changed the namespace
         if (version_compare(PHPUnitVersion::series(), '10.3', '>=')) {
             $generatorClass = new Generator();

tests/StubTest.php

@@ -19,6 +19,7 @@ final class StubTest extends TestCase
 
     public function setUp(): void
     {
+        require_once $file = __DIR__. '/_data/DummyAbstractClass.php';
         require_once $file = __DIR__. '/_data/DummyOverloadableClass.php';
         require_once $file = __DIR__. '/_data/DummyClass.php';
         $this->dummy = new DummyClass(true);
@@ -404,6 +405,17 @@ public function testStubMakeEmptyInterface()
         $stub = Stub::makeEmpty(Countable::class, ['count' => 5]);
         $this->assertEquals(5, $stub->count());
     }
+
+    public function testStubMakeEmptyAbstractClass()
+    {
+        if (version_compare(PHPUnitVersion::id(), '12', '>=')) {
+            $this->expectException(RuntimeException::class);
+            $this->expectExceptionMessage('PHPUnit 12 or greater does not allow to mock abstract classes anymore');
+        }
+
+        $stub = Stub::make('DummyAbstractClass');
+        $this->assertInstanceOf('DummyAbstractClass', $stub);
+    }
 }
 
 class MyClassWithPrivateProperties

tests/_data/DummyAbstractClass.php

@@ -0,0 +1,7 @@
+<?php
+
+declare(strict_types=1);
+
+abstract class DummyAbstractClass
+{
+}