Make test robust to R configuration/version/platform issue (#5867)

inst/tests/tests.Rraw

@@ -135,12 +135,17 @@ if (!test_longdouble) {
 # generate simple error messages from base that are checked against in our tests. this helps
 #   protect us against these messages evolving in base in the future, and against these messages
 #   potentially not being produced in English.
+# If the target condition only appears on certain platforms/R versions, this will return NULL
+#   whenever the code succeeds, or the message matcher wherever it fails. Thus we can flexibly
+#   pass e.g. 'warning = NULL | warning = <warning>' concisely as 'test(., warning = get_msg())'.
 # Three use cases:
 #   (1) match message exactly [missing delim]
 #   (2) match message pattern after dropping anything between delimeters [delim, fmt=FALSE]
 #   (3) function factory for matching messages exactly by substituting anything between delimeters [delim, fmt=TRUE]
 get_msg = function(e, delim, fmt=FALSE) {
-  msg = tryCatch(e, error=identity, warning=identity)$message
+  condition = tryCatch({e; NULL}, error=identity, warning=identity)
+  if (is.null(condition)) return(condition)
+  msg = condition$message
   if (missing(delim)) return(msg)
   if (length(delim) == 1L) delim[2L] = delim[1L]
   msg = gsub(
@@ -165,7 +170,8 @@ base_messages = list(
   missing_file = get_msg({tmp <- tempfile(tmpdir=tempfile("xxx")); file(tmp, "w")}, "'"),
   # gives both error & warning but tryCatch returns the warning first, so suppress
   cant_open_file = get_msg(suppressWarnings({con<-file(tempfile()); open(con, 'r')})),
-  mixed_subscripts = get_msg(letters[-1:1])
+  mixed_subscripts = get_msg(letters[-1:1]),
+  maybe_invalid_old_posixct = get_msg(as.POSIXct("1893-12-28 05:15:36", tz = ""))
 )
 
 ##########################
@@ -16854,8 +16860,17 @@ if (.Platform$OS.type!="windows") {
   # blank TZ env variable on non-Windows is recognized as UTC consistent with C and R; but R's tz= argument is the opposite and uses "" for local
 }
 Sys.unsetenv("TZ")
-tt = fread(tmp, colClasses=list(POSIXct="times"), tz="")   # from v1.14.0 tz="" needed
-test(2150.025, attr(tt$times, "tzone"), "") # as.POSIXct puts "" on the result (testing the write.csv version here with missing tzone)
+# Notes:
+#  - from v1.14.0 tz="" needed
+#  - as.POSIXct puts "" on the result (testing the write.csv version here with missing tzone)
+#  - Per #5866, this test is complicated by some interaction with very specific builds of R where
+#    as.POSIXct() might fail for very old timestamps when 'tz=""' is used. On such systems,
+#    as.POSIXct() failure means 'times' is returned as a character, hence no 'tzone' attribute.
+#    fread() will also throw a warning, one substring of which will be the reproduced base R error.
+test(2150.025,
+     attr(fread(tmp, colClasses=list(POSIXct="times"), tz="")$times, "tzone"),
+     if (is.null(base_messages$maybe_invalid_old_posixct)) "" else NULL,
+     warning=base_messages$maybe_invalid_old_posixct)
 # the times will be different though here because as.POSIXct read them as local time.
 if (is.na(oldtz)) Sys.unsetenv("TZ") else Sys.setenv(TZ=oldtz)
 fwrite(copy(DT)[ , times := format(times, '%FT%T+00:00')], tmp)