[TASK] Add unit test for first method in Typo3VersionService

extensions/ter_fe2/Tests/Unit/Service/Typo3VersionServiceTest.php

+<?php
+declare(strict_types = 1);
+namespace T3o\TerFe2\Tests\Service;
+
+/*
+ * This file is part of TYPO3 CMS-extension "ter_fe2".
+ *
+ * It is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License, either version 2
+ * of the License, or any later version.
+ */
+
+use Nimut\TestingFramework\TestCase\AbstractTestCase;
+use T3o\TerFe2\Service\Typo3VersionService;
+
+class Typo3VersionServiceTest extends AbstractTestCase
+{
+
+    /**
+     * @test
+     */
+    public function getAllMajorVersionsReturnsArrayWithMultipleMajorVersions()
+    {
+        $majorVersions = Typo3VersionService::getAllMajorVersions();
+
+        self::assertNotEmpty(
+            $majorVersions
+        );
+        self::assertIsArray(
+            $majorVersions
+        );
+        self::assertArrayHasKey(
+            0,
+            $majorVersions
+        );
+        self::assertIsArray(
+            $majorVersions[0]
+        );
+    }
+
+}