Add test for bug #52480

ext/date/tests/bug52480.phpt

@@ -0,0 +1,26 @@
+--TEST--
+Bug #52480 (Incorrect difference using DateInterval)
+--XFAIL--
+See https://bugs.php.net/bug.php?id=52480
+--FILE--
+<?php
+
+$expectedDiff = (array) new DateInterval('P30D');
+
+// If the DateInterval object was created by DateTime::diff(), then this is the total
+// number of days between the start and end dates. Otherwise, days will be FALSE.
+// https://secure.php.net/manual/en/class.dateinterval.php
+$expectedDiff['days'] = 30;
+
+foreach (DateTimeZone::listIdentifiers() as $timezone) {
+    $start = new DateTime('2017-03-01', new DateTimeZone($timezone));
+    $end = new DateTime('2017-03-31', new DateTimeZone($timezone));
+
+    if ($expectedDiff != (array) $start->diff($end)) {
+        echo "\nWrong result for $timezone!\n";
+    }
+}
+?>
+===DONE===
+--EXPECT--
+===DONE===