TestSuiteLoader will always consider classes from the current file

tests/PHPUnit/CustomTestCase/ChildTest.php

@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\CustomTestCase;
+
+class ChildTest extends ParentTest
+{
+    private function getEntity(): bool
+    {
+        return true;
+    }
+}

tests/PHPUnit/CustomTestCase/ParentTest.php

@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\CustomTestCase;
+
+use function PHPUnit\Framework\assertTrue;
+use PHPUnit\Framework\TestCase;
+
+class ParentTest extends TestCase
+{
+    private function getEntity(): bool
+    {
+        return false;
+    }
+
+    /** @test */
+    public function testOverrideMethod(): void
+    {
+        assertTrue($this->getEntity() || true);
+    }
+}