Improve current_date function testing

The test was only using TZ with positive shift, this change
allows to test if the code works properly for negative shift as well.

presto-main/src/test/java/com/facebook/presto/operator/scalar/TestDateTimeFunctions.java

@@ -31,6 +31,7 @@
 import org.joda.time.DateTimeZone;
 import org.joda.time.LocalTime;
 import org.joda.time.ReadableInstant;
+import org.joda.time.chrono.ISOChronology;
 import org.testng.annotations.Test;
 
 import java.time.Instant;
@@ -119,8 +120,13 @@ public void testCurrentDateTimezone()
             throws Exception
     {
         TimeZoneKey kievTimeZoneKey = getTimeZoneKey("Europe/Kiev");
-        for (long instant = new DateTime(2000, 6, 15, 0, 0).getMillis(); instant < new DateTime(2016, 6, 15, 0, 0).getMillis(); instant += TimeUnit.HOURS.toMillis(1)) {
+        TimeZoneKey montrealTimeZoneKey = getTimeZoneKey("America/Montreal");
+        // We expect UTC millis later on so we have to use UTC chronology
+        for (long instant = ISOChronology.getInstanceUTC().getDateTimeMillis(2000, 6, 15, 0, 0, 0, 0);
+             instant < ISOChronology.getInstanceUTC().getDateTimeMillis(2016, 6, 15, 0, 0, 0, 0);
+             instant += TimeUnit.HOURS.toMillis(1)) {
             assertCurrentDateAtInstant(kievTimeZoneKey, instant);
+            assertCurrentDateAtInstant(montrealTimeZoneKey, instant);
             assertCurrentDateAtInstant(TIME_ZONE_KEY, instant);
         }
     }