added unit tests

tests/Support/JsonErrorResponse.php

@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Support;
+
+use RuntimeException;
+
+/** Thrown instead of exit() when QDB_TESTING is defined. */
+final class JsonErrorResponse extends RuntimeException
+{
+    public function __construct(
+        public readonly string $errorCode,
+        public readonly string $errorMessage,
+        public readonly int $httpStatus = 400,
+        public readonly mixed $details = null,
+    ) {
+        parent::__construct($errorMessage, $httpStatus);
+    }
+}