added unit tests

tests/Unit/EncryptedPayloadTest.php

@@ -0,0 +1,37 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit;
+
+use InvalidArgumentException;
+use PHPUnit\Framework\TestCase;
+
+final class EncryptedPayloadTest extends TestCase
+{
+    public function testEnvelopeRoundTrip(): void
+    {
+        require_once dirname(__DIR__, 2) . '/lib/encrypted_payload.php';
+        $token = bin2hex(random_bytes(32));
+        $json = '{"clientCode":"X","answers":[]}';
+        $env = qdb_sensitive_envelope($json, $token);
+        $this->assertTrue($env['encrypted']);
+        $plain = qdb_decrypt_sensitive_envelope($env, $token);
+        $this->assertSame($json, $plain);
+    }
+
+    public function testWrongTokenFailsDecrypt(): void
+    {
+        require_once dirname(__DIR__, 2) . '/lib/encrypted_payload.php';
+        $env = qdb_sensitive_envelope('{}', bin2hex(random_bytes(32)));
+        $this->expectException(\Exception::class);
+        qdb_decrypt_sensitive_envelope($env, bin2hex(random_bytes(32)));
+    }
+
+    public function testInvalidEnvelopeRejected(): void
+    {
+        require_once dirname(__DIR__, 2) . '/lib/encrypted_payload.php';
+        $this->expectException(InvalidArgumentException::class);
+        qdb_decrypt_sensitive_envelope(['encrypted' => false], bin2hex(random_bytes(8)));
+    }
+}