Add adjustTime to FrozenClock

src/FrozenClock.php

@@ -5,6 +5,7 @@
 
 use DateTimeImmutable;
 use DateTimeZone;
+use Throwable;
 
 final class FrozenClock implements Clock
 {
@@ -22,6 +23,30 @@ public function setTo(DateTimeImmutable $now): void
         $this->now = $now;
     }
 
+    /**
+     * Adjusts the current time by a given time interval.
+     *
+     * @param string $timeInterval @see https://www.php.net/manual/en/datetime.formats.php
+     *
+     * @throws MalformedDateString When an invalid date/time string is passed (PHP 8.3+).
+     */
+    public function adjustTime(string $timeInterval): void
+    {
+        try {
+            $this->now = $this->now->modify($timeInterval);
+        } catch (Throwable) {
+            /*
+             * PHP 8.3+ throws `DateMalformedStringException` when an invalid date/time string
+             * is passed to `DateTimeImmutable::modify()`.
+             * PHP 8.2 and below do not throw an exception, but return `false`.
+             *
+             * In order to maintain compatibility with PHP 8.2 and below, we catch all exceptions,
+             * including `TypeError`, throwing a custom exception for compatibility’s sake.
+             */
+            throw new MalformedDateString();
+        }
+    }
+
     public function now(): DateTimeImmutable
     {
         return $this->now;

src/MalformedDateString.php

@@ -0,0 +1,10 @@
+<?php
+declare(strict_types=1);
+
+namespace Lcobucci\Clock;
+
+use Exception;
+
+class MalformedDateString extends Exception
+{
+}

test/FrozenClockTest.php

@@ -34,6 +34,34 @@ public function nowSetChangesTheObject(): void
         self::assertSame($newNow, $clock->now());
     }
 
+    #[Test]
+    public function adjustTimeChangesTheObject(): void
+    {
+        $oldNow = new DateTimeImmutable();
+        $newNow = $oldNow->modify('+1 day');
+
+        $clock = new FrozenClock($oldNow);
+
+        $clock->adjustTime('+1 day');
+
+        self::assertNotEquals($oldNow, $clock->now());
+        self::assertEquals($newNow, $clock->now());
+
+        $clock->adjustTime('-1 day');
+
+        self::assertEquals($oldNow, $clock->now());
+        self::assertNotEquals($newNow, $clock->now());
+    }
+
+    #[Test]
+    public function adjustTimeThrowsForInvalidTimeInterval(): void
+    {
+        $clock = FrozenClock::fromUTC();
+
+        $this->expectException(MalformedDateString::class);
+        $clock->adjustTime('invalid');
+    }
+
     #[Test]
     public function fromUTCCreatesClockFrozenAtCurrentSystemTimeInUTC(): void
     {