diff --git a/src/ProcessManager.php b/src/ProcessManager.php
index 1ff9f1ff..f47d7779 100644
--- a/src/ProcessManager.php
+++ b/src/ProcessManager.php
@@ -32,6 +32,8 @@ class ProcessManager
 
     private static string $input = '';
 
+    private static ?ExecutableFinder $executableFinder = null;
+
     /** @var array Secrets to redact from error messages */
     private array $secrets = [];
 
@@ -81,14 +83,19 @@ public static function setBin(string $bin): void
         self::$bin = $bin;
     }
 
+    public static function setExecutableFinder(?ExecutableFinder $executableFinder): void
+    {
+        self::$executableFinder = $executableFinder;
+    }
+
     public static function guessBin(): string
     {
         if (isset(self::$bin) && self::$bin !== '') {
             return self::$bin;
         }
 
-        $finder = new ExecutableFinder();
-        $rclonePath = $finder->find('rclone', '/usr/bin/rclone', [
+        $finder = self::$executableFinder ?? new ExecutableFinder();
+        $rclonePath = $finder->find('rclone', null, [
             '/usr/local/bin',
             '/usr/bin',
             '/bin',
diff --git a/tests/Unit/ProcessManagerTest.php b/tests/Unit/ProcessManagerTest.php
new file mode 100644
index 00000000..d563bd0f
--- /dev/null
+++ b/tests/Unit/ProcessManagerTest.php
@@ -0,0 +1,52 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Verseles\Flyclone\Tests\Unit;
+
+use PHPUnit\Framework\TestCase;
+use RuntimeException;
+use Symfony\Component\Process\ExecutableFinder;
+use Verseles\Flyclone\ProcessManager;
+
+class ProcessManagerTest extends TestCase
+{
+    protected function tearDown(): void
+    {
+        // Reset static state
+        ProcessManager::setBin('');
+        ProcessManager::setExecutableFinder(null);
+        parent::tearDown();
+    }
+
+    public function testGuessBinThrowsExceptionWhenRcloneNotFound(): void
+    {
+        $mockFinder = $this->createMock(ExecutableFinder::class);
+        $mockFinder->expects($this->once())
+            ->method('find')
+            ->with('rclone', null, $this->anything())
+            ->willReturn(null);
+
+        ProcessManager::setExecutableFinder($mockFinder);
+
+        $this->expectException(RuntimeException::class);
+        $this->expectExceptionMessage('Rclone binary not found');
+
+        ProcessManager::guessBin();
+    }
+
+    public function testGuessBinReturnsPathWhenFound(): void
+    {
+        $mockFinder = $this->createMock(ExecutableFinder::class);
+        $mockFinder->expects($this->once())
+            ->method('find')
+            ->with('rclone', null, $this->anything())
+            ->willReturn('/usr/bin/rclone');
+
+        ProcessManager::setExecutableFinder($mockFinder);
+
+        $bin = ProcessManager::guessBin();
+
+        $this->assertSame('/usr/bin/rclone', $bin);
+    }
+}