Add modify and default constructor to FrozenClock

src/FrozenClock.php

@@ -8,7 +8,7 @@
 
 final class FrozenClock implements Clock
 {
-    public function __construct(private DateTimeImmutable $now)
+    public function __construct(private DateTimeImmutable $now = new DateTimeImmutable())
     {
     }
 
@@ -22,6 +22,11 @@ public function setTo(DateTimeImmutable $now): void
         $this->now = $now;
     }
 
+    public function modify(string $modify): void
+    {
+        $this->now = $this->now->modify($modify);
+    }
+
     public function now(): DateTimeImmutable
     {
         return $this->now;

test/FrozenClockTest.php

@@ -34,6 +34,25 @@ public function nowSetChangesTheObject(): void
         self::assertSame($newNow, $clock->now());
     }
 
+    #[Test]
+    public function modifyChangesTheObject(): void
+    {
+        $oldNow = new DateTimeImmutable();
+        $newNow = $oldNow->modify('+1 day');
+
+        $clock  = new FrozenClock($oldNow);
+
+        $clock->modify('+1 day');
+
+        self::assertNotEquals($oldNow, $clock->now());
+        self::assertEquals($newNow, $clock->now());
+
+        $clock->modify('-1 day');
+
+        self::assertEquals($oldNow, $clock->now());
+        self::assertNotEquals($newNow, $clock->now());
+    }
+
     #[Test]
     public function fromUTCCreatesClockFrozenAtCurrentSystemTimeInUTC(): void
     {