[Fix #219] In interval use UTC when tzone is missing.

   Complies with the value returned by `tz`.

R/intervals.r

@@ -235,7 +235,7 @@ setMethod("$<-", signature(x = "Interval"), function(x, name, value) {
 #' # 2009-01-01 UTC--2009-02-01 UTC 
 new_interval <- interval <- function(start, end, tzone = attr(start, "tzone")){
 	if (is.null(tzone)) {
-		if (is.null(attr(end, "tzone"))) tzone <- ""
+		if (is.null(attr(end, "tzone"))) tzone <- "UTC"
 		else tzone <- attr(end, "tzone")
 	}
 

inst/tests/test-intervals.R

@@ -111,6 +111,11 @@ test_that("format.Interval correctly displays intervals of length 0", {
   expect_output(int[FALSE], "Interval\\(0)")
 })
 
+test_that("interval handles correctly time zones of Date objects", {
+  expect_equal(interval(as.Date('2011-01-01'), as.Date('2013-01-01')),
+               new_interval(ymd('2011-01-01'), ymd('2013-01-01')))
+})
+
 test_that("summary.Interval creates useful summary", {
   int <- interval(ymd(20090201), ymd(20090101))
   text <- c(3, "2009-01-01", "2009-02-01", "UTC", 1)