From 40d45ede416fc241f0820a0dcd94569dda0a7e88 Mon Sep 17 00:00:00 2001
From: "Eloy Lafuente (stronk7)" <stronk7@moodle.org>
Date: Sun, 28 Mar 2021 14:01:22 +0200
Subject: [PATCH] MDL-56609 phpunit: Fix bogus expectation on DST changes day

Current test works ok every day of the year but the day of
DST begin changes (last Sunday of March currently).

That day, 01:00 Europe/London simply doesn't exist, because
the time is moved forward by 60 minutes.

Hence the expectation for the next cron execution is not 1 "normal"
day (24h) but 1 less hour.

Note this only happens for the current test on DST begins, the
opposite change (DST ends), happening the last Sunday of October
is not affected, because, at all effects, 01:00 is a perfectly normal
and existing hour.
---
 lib/tests/scheduled_task_test.php | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/lib/tests/scheduled_task_test.php b/lib/tests/scheduled_task_test.php
index 24ac7d4e583..b378a96f70b 100644
--- a/lib/tests/scheduled_task_test.php
+++ b/lib/tests/scheduled_task_test.php
@@ -56,20 +56,40 @@ class core_scheduled_task_testcase extends advanced_testcase {
 
         $this->setTimezone('Europe/London');
 
+        // Let's specify the hour we are going to use initially for the test.
+        // (note that we pick 01:00 that is tricky for Europe/London, because
+        // it's exactly the Daylight Saving Time Begins hour.
+        $testhour = 1;
+
         // Test job run at 1 am.
         $testclass = new \core\task\scheduled_test_task();
 
         // All fields default to '*'.
-        $testclass->set_hour('1');
+        $testclass->set_hour($testhour);
         $testclass->set_minute('0');
         // Next valid time should be 1am of the next day.
         $nexttime = $testclass->get_next_scheduled_time();
 
         $oneamdate = new DateTime('now', new DateTimeZone('Europe/London'));
-        $oneamdate->setTime(1, 0, 0);
+        $oneamdate->setTime($testhour, 0, 0);
+
+        // Once a year (currently last Sunday of March), when changing to Daylight Saving Time,
+        // Europe/London 01:00 simply doesn't exists because, exactly at 01:00 the clock
+        // is advanced by one hour and becomes 02:00. When that happens, the DateInterval
+        // calculations cannot be to advance by 1 day, but by one less hour. That is exactly when
+        // the next scheduled run will happen (next day 01:00).
+        $isdaylightsaving = false;
+        if ($testhour < (int)$oneamdate->format('H')) {
+            $isdaylightsaving = true;
+        }
+
         // Make it 1 am tomorrow if the time is after 1am.
         if ($oneamdate->getTimestamp() < time()) {
             $oneamdate->add(new DateInterval('P1D'));
+            if ($isdaylightsaving) {
+                // If today is Europe/London Daylight Saving Time Begins, expectation is 1 less hour.
+                $oneamdate->sub(new DateInterval('PT1H'));
+            }
         }
         $oneam = $oneamdate->getTimestamp();