diff --git a/src/Command/SelfUpdateCommand.php b/src/Command/SelfUpdateCommand.php
index 1a3322ac..be5a9c88 100644
--- a/src/Command/SelfUpdateCommand.php
+++ b/src/Command/SelfUpdateCommand.php
@@ -93,13 +93,16 @@ protected function execute(InputInterface $input, OutputInterface $output): int
     }
 
     /**
+     * Calculate the full path where the old PHAR file will be backup (to be able to roll back to it).
+     *
+     * @param string|null $directory The directory where the backup will be stored.
      * @return string
      */
-    protected function getBackupPath(): string
+    protected function getBackupPath(?string $directory = null): string
     {
-        $directory = getenv('HOME');
+        $directory = $directory ?? getenv('HOME'); // Default to $HOME as base directory if not provided.
         if (empty($directory) || !is_dir($directory)) {
-            throw new \RuntimeException('Your $HOME enviroment variable is either not set or is not a directory');
+            throw new \RuntimeException("The {$directory} path is not an existing directory");
         }
         $directory .= '/.moodle-plugin-ci';
 
diff --git a/tests/Command/SelfUpdateCommandTest.php b/tests/Command/SelfUpdateCommandTest.php
new file mode 100644
index 00000000..4c28e3b8
--- /dev/null
+++ b/tests/Command/SelfUpdateCommandTest.php
@@ -0,0 +1,63 @@
+<?php
+
+/*
+ * This file is part of the Moodle Plugin CI package.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ *
+ * @copyright 2023 onwards Eloy Lafuente (stronk7) {@link https://stronk7.com}
+ * @license https://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later.
+ */
+
+namespace Command;
+
+use MoodlePluginCI\Command\SelfUpdateCommand;
+use Symfony\Component\Filesystem\Filesystem;
+
+/**
+ * Tests for the SelfUpdateCommand class.
+ *
+ * There isn't much to test here, only helper methods. Note that the utility itself
+ * will be covered by some integration tests @ CIs.
+ */
+class SelfUpdateCommandTest extends \PHPUnit\Framework\TestCase
+{
+    /**
+     * @covers \MoodlePluginCI\Command\SelfUpdateCommand::getBackupPath
+     */
+    public function testGetBackupPathNotExists()
+    {
+        $command = new SelfUpdateCommand();
+
+        // Try with a non-existing directory.
+        $rollBackDir = sys_get_temp_dir() . '/not_existing_dir';
+        $rollBackFile = $rollBackDir . '/.moodle-plugin-ci/moodle-plugin-ci-old.phar';
+
+        $this->expectException(\RuntimeException::class);
+
+        // Use reflection to test the protected method.
+        $method = new \ReflectionMethod($command, 'getBackupPath');
+        $method->setAccessible(true);
+        $this->assertSame($rollBackFile, $method->invoke($command, $rollBackDir));
+    }
+
+    /**
+     * @covers \MoodlePluginCI\Command\SelfUpdateCommand::getBackupPath
+     */
+    public function testGetBackupPathExists()
+    {
+        $command = new SelfUpdateCommand();
+
+        // Try with a existing directory.
+        $rollBackDir = sys_get_temp_dir() . '/existing_dir';
+        (new Filesystem())->mkdir($rollBackDir); // Let's create the directory.
+        $rollBackFile = $rollBackDir . '/.moodle-plugin-ci/moodle-plugin-ci-old.phar';
+
+
+        // Use reflection to test the protected method.
+        $method = new \ReflectionMethod($command, 'getBackupPath');
+        $method->setAccessible(true);
+        $this->assertSame($rollBackFile, $method->invoke($command, $rollBackDir));
+    }
+}