MDL-85563 phpunit: Clock API should always use Moodle system time

When using `clock::now()` the frozen cloxk and incrementing clock will now
always return a `DateTimeImmutable` that uses the configured Moodle system
time. In unit tests this will be Australia/Perth.

Before this change, it would sometimes be UCT.

lib/phpunit/tests/advanced_test.php

@@ -781,6 +781,7 @@ final class advanced_test extends \advanced_testcase {
         $this->assertEquals(0, $mockedclock->now()->getTimestamp());
         $this->assertEquals(1, $newclock->now()->getTimestamp());
         $this->assertEquals(2, $mockedclock->now()->getTimestamp());
+        $this->assertEquals('Australia/Perth', $newclock->now()->getTimezone()->getName());
 
         // Specify a specific start time.
         $newclock = $this->mock_clock_with_incrementing(12345);
@@ -792,6 +793,7 @@ final class advanced_test extends \advanced_testcase {
         $this->assertEquals(12347, $mockedclock->now()->getTimestamp());
 
         $this->assertEquals($newclock->time, $mockedclock->now()->getTimestamp());
+        $this->assertEquals('Australia/Perth', $newclock->now()->getTimezone()->getName());
     }
 
     /**
@@ -814,6 +816,7 @@ final class advanced_test extends \advanced_testcase {
         $initialtime = $mockedclock->now()->getTimestamp();
         $this->assertEquals($initialtime, $newclock->now()->getTimestamp());
         $this->assertEquals($initialtime, $mockedclock->now()->getTimestamp());
+        $this->assertEquals('Australia/Perth', $newclock->now()->getTimezone()->getName());
 
         // Specify a specific start time.
         $newclock = $this->mock_clock_with_frozen(12345);
@@ -824,5 +827,6 @@ final class advanced_test extends \advanced_testcase {
         $this->assertEquals($initialtime, $mockedclock->now());
         $this->assertEquals($initialtime, $newclock->now());
         $this->assertEquals($initialtime, $mockedclock->now());
+        $this->assertEquals('Australia/Perth', $newclock->now()->getTimezone()->getName());
     }
 }

lib/testing/classes/frozen_clock.php

@@ -40,7 +40,7 @@ class frozen_clock implements \core\clock {
             $this->time = (new \DateTimeImmutable("@{$time}"))
                 ->setTimezone(\core_date::get_server_timezone_object());
         } else {
-            $this->time = new \DateTimeImmutable();
+            $this->time = (new \DateTimeImmutable())->setTimezone(\core_date::get_server_timezone_object());
         }
     }
 

lib/testing/classes/incrementing_clock.php

@@ -26,6 +26,9 @@ class incrementing_clock implements \core\clock {
     /** @var int The next time of the clock */
     public int $time;
 
+    /** @var DateTimeZone The system timezone. */
+    protected DateTimeZone $timezone;
+
     /**
      * Create a new instance of the incrementing clock.
      *
@@ -35,10 +38,11 @@ class incrementing_clock implements \core\clock {
         ?int $starttime = null,
     ) {
         $this->time = $starttime ?? time();
+        $this->timezone = \core_date::get_server_timezone_object();
     }
 
     public function now(): \DateTimeImmutable {
-        return new \DateTimeImmutable('@' . $this->time++);
+        return (new \DateTimeImmutable('@' . $this->time++))->setTimezone($this->timezone);
     }
 
     public function time(): int {