Add test for abstract test case class without Test suffix in class name

tests/_files/AbstractTestCase.php

@@ -0,0 +1,20 @@
+<?php declare(strict_types=1);
+/*
+ * This file is part of PHPUnit.
+ *
+ * (c) Sebastian Bergmann <sebastian@phpunit.de>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+namespace PHPUnit\TestFixture;
+
+use PHPUnit\Framework\TestCase;
+
+abstract class AbstractTestCase extends TestCase
+{
+    public function testOne(): void
+    {
+        $this->assertTrue(true);
+    }
+}

tests/end-to-end/generic/abstract-test-class-without-test-suffix.phpt

@@ -0,0 +1,27 @@
+--TEST--
+phpunit ../../_files/AbstractTestCase.php
+--FILE--
+<?php declare(strict_types=1);
+$_SERVER['argv'][] = '--do-not-cache-result';
+$_SERVER['argv'][] = '--no-configuration';
+$_SERVER['argv'][] = 'AbstractTestCase';
+$_SERVER['argv'][] = __DIR__ . '/../../_files/AbstractTestCase.php';
+
+require_once __DIR__ . '/../../bootstrap.php';
+PHPUnit\TextUI\Command::main();
+--EXPECTF--
+PHPUnit %s by Sebastian Bergmann and contributors.
+
+Warning:       Invocation with class name is deprecated
+
+W                                                                   1 / 1 (100%)
+
+Time: %s, Memory: %s
+
+There was 1 warning:
+
+1) Warning
+Cannot instantiate class "PHPUnit\TestFixture\AbstractTestCase".
+
+WARNINGS!
+Tests: 1, Assertions: 0, Warnings: 1.