Require filename

On second thought, a filename should be required, otherwise the object would need to be serialized and sent to another process to be of any use.

lib/FileMutex.php

@@ -30,14 +30,9 @@ class FileMutex implements Mutex {
     /**
      * Creates a new mutex.
      *
-     * @param string|null Optional file name. If one is not provided a temporary file is created in the system temporary
-     *    file directory.
+     * @param string|null
      */
-    public function __construct(string $fileName = null) {
-        if ($fileName === null) {
-            $fileName = \tempnam(\sys_get_temp_dir(), 'mutex-') . '.lock';
-        }
-
+    public function __construct(string $fileName) {
         $this->fileName = $fileName;
     }
 

test/FileMutexTest.php

@@ -7,6 +7,6 @@
 
 class FileMutexTest extends AbstractMutexTest {
     public function createMutex(): Mutex {
-        return new FileMutex;
+        return new FileMutex(\tempnam(\sys_get_temp_dir(), 'mutex-') . '.lock');
     }
 }