Fix deprecation warning if trailing slash in path is omitted

src/TextUI/Command.php

@@ -783,7 +783,8 @@ protected function handleArguments(array $argv): void
         if (isset($this->options[1][0]) &&
             \substr($this->options[1][0], -5, 5) !== '.phpt' &&
             \substr($this->options[1][0], -4, 4) !== '.php' &&
-            \substr($this->options[1][0], -1, 1) !== '/') {
+            \substr($this->options[1][0], -1, 1) !== '/' &&
+            !\is_dir($this->options[1][0])) {
             $this->arguments['warnings'][] = 'Invocation with class name is deprecated';
         }
 

tests/end-to-end/regression/GitHub/3983-2.phpt

@@ -0,0 +1,17 @@
+--TEST--
+phpunit 3983/
+--FILE--
+<?php declare(strict_types=1);
+$_SERVER['argv'][1] = '--no-configuration';
+$_SERVER['argv'][2] = __DIR__ . '/3983/';
+
+require __DIR__ . '/../../../bootstrap.php';
+PHPUnit\TextUI\Command::main();
+--EXPECTF--
+PHPUnit %s by Sebastian Bergmann and contributors.
+
+.                                                                   1 / 1 (100%)
+
+Time: %s, Memory: %s
+
+OK (1 test, 1 assertion)

tests/end-to-end/regression/GitHub/3983.phpt

@@ -0,0 +1,17 @@
+--TEST--
+phpunit 3983/
+--FILE--
+<?php declare(strict_types=1);
+$_SERVER['argv'][1] = '--no-configuration';
+$_SERVER['argv'][2] = __DIR__ . '/3983';
+
+require __DIR__ . '/../../../bootstrap.php';
+PHPUnit\TextUI\Command::main();
+--EXPECTF--
+PHPUnit %s by Sebastian Bergmann and contributors.
+
+.                                                                   1 / 1 (100%)
+
+Time: %s, Memory: %s
+
+OK (1 test, 1 assertion)

tests/end-to-end/regression/GitHub/3983/Issue3983Test.php

@@ -0,0 +1,18 @@
+<?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.
+ */
+use PHPUnit\Framework\TestCase;
+
+final class Issue3983Test extends TestCase
+{
+    public function testOne(): void
+    {
+        $this->assertTrue(true);
+    }
+}