Add tests for autogenerated IDs

tests/integration/NumDocument.php

@@ -0,0 +1,11 @@
+<?php declare(strict_types=1);
+
+namespace Test\Integration;
+
+/**
+ * A test document with a numeric ID
+ */
+class NumDocument
+{
+    public function __construct(public int $id = 0, public string $value = '') { }
+}