return utc from clock

tests/Fakes/FakeClock.php

@@ -4,12 +4,15 @@ namespace Tests\Fakes;
 
 use App\Auth\Clock;
 use DateTimeImmutable;
+use InvalidArgumentException;
 
 class FakeClock implements Clock
 {
     public function __construct(
         private DateTimeImmutable $currentTime,
-    ) {}
+    ) {
+        $this->assertUtc($currentTime);
+    }
 
     public function now(): DateTimeImmutable
     {
@@ -18,6 +21,16 @@ class FakeClock implements Clock
 
     public function setTime(DateTimeImmutable $newTime): void
     {
+        $this->assertUtc($newTime);
         $this->currentTime = $newTime;
     }
+
+    private function assertUtc(DateTimeImmutable $time): void
+    {
+        if ($time->getTimezone()->getOffset($time) !== 0) {
+            throw new InvalidArgumentException(
+                'FakeClock requires a DateTimeImmutable in UTC.'
+            );
+        }
+    }
 }