Add unit tests for .xts() checking index class and timezone

As documented in #249, v0.11 introduced changes to .xts() which altered
behaviour compared to v0.10-2.  As a first step to fixing this
regression, this commit adds unit tests for all possible permutations
for setting the index class and timezone in .xts().

The tests check accessing the class in 3 different ways:
    1. Using tclass()
    2. Using indexClass()
    3. Checking the 'tclass' attribute on the index object

Similarly the tests check accessing timezone by:
    1. Using tzone()
    2. Using indexTZ()
    3. Checking the '.indexTZ' attribute on the index object

These tests are designed to document the behaviour as of v0.10-2.  As
such they pass on v0.10-2 but fail for v0.11.

inst/unitTests/runit.xts.R

@@ -50,3 +50,48 @@ test..xts_dimnames_in_dots <- function() {
   y <- xts(1:5, index(x), dimnames = list(NULL, "x"))
   checkEquals(x, y)
 }
+
+checkXtsClass <- function(xts, class) {
+  checkEquals(tclass(xts), class)
+  checkEquals(indexClass(xts), class)
+  checkEquals(attr(attr(xts, "index"), "tclass"), class)
+}
+
+### Check that .indexCLASS takes precedence over tclass when both specified
+test..xts_class <- function() {
+  checkXtsClass(.xts(1, 1), c("POSIXct", "POSIXt"))
+  checkXtsClass(.xts(1, 1, tclass="timeDate"), "timeDate")
+  checkXtsClass(.xts(1, 1, .indexCLASS="Date"), "Date")
+  checkXtsClass(.xts(1, 1, tclass="timeDate", .indexCLASS="Date"), "Date")
+
+  ## also check that tclass is ignored if specified as part of index
+  checkXtsClass(.xts(1, structure(1, tzone="",tclass="yearmon")), c("POSIXct", "POSIXt"))
+  checkXtsClass(.xts(1, structure(1, tzone="",tclass="yearmon"), tclass="timeDate"), "timeDate")
+  checkXtsClass(.xts(1, structure(1, tzone="",tclass="yearmon"), .indexCLASS="Date"), "Date")
+  checkXtsClass(.xts(1, structure(1, tzone="",tclass="yearmon"), tclass="timeDate", .indexCLASS="Date"), "Date")
+}
+
+checkXtsTz <- function(xts, tzone) {
+  checkEquals(tzone(xts), tzone)
+  checkEquals(indexTZ(xts), tzone)
+  checkEquals(attr(attr(xts, "index"), "tzone"), tzone)
+}
+
+.setUp <- function() {
+  Sys.setenv(TZ="UTC")
+}
+
+### Check that tzone is honoured and .indexTZ ignored
+test..xts_tzone <- function() {
+  checkXtsTz(.xts(1, 1), "UTC")
+  checkXtsTz(.xts(1, 1, tzone="Europe/London"), "Europe/London")
+  ## this case passes in 0.10-2 but looks wrong
+  checkXtsTz(.xts(1, 1, .indexTZ="America/New_York"), "UTC")
+  checkXtsTz(.xts(1, 1, tzone="Europe/London", .indexTZ="America/New_York"), "Europe/London")
+
+  ## Cases where tzone is specified in the index
+  checkXtsTz(.xts(1, structure(1, tzone="Asia/Tokyo",tclass="yearmon")), "Asia/Tokyo")
+  checkXtsTz(.xts(1, structure(1, tzone="Asia/Tokyo",tclass="yearmon"), tzone="Europe/London"), "Europe/London")
+  checkXtsTz(.xts(1, structure(1, tzone="Asia/Tokyo",tclass="yearmon"), .indexTZ="America/New_York"), "Asia/Tokyo")
+  checkXtsTz(.xts(1, structure(1, tzone="Asia/Tokyo",tclass="yearmon"), tzone="Europe/London", .indexTZ="America/New_York"), "Europe/London")
+}