Fix handling of -Inf aicc in ETS()

Resolves #425

Author: mitchelloharawild

R/ets.R

@@ -67,10 +67,13 @@ train_ets <- function(.data, specials, opt_crit,
     }
     new <- new$result
 
-    if ((new[[ic]] %||% Inf) < (best[[ic]] %||% Inf) && is.finite(new[[ic]]) || is.null(best)) {
+    
+    new_ic <- if(isTRUE(is.finite(new[[ic]]))) new[[ic]] else Inf
+    
+    if (new_ic < (best[[ic]] %||% Inf) || is.null(best)) {
       best <<- new
     }
-    new[[ic]] %||% Inf
+    new_ic
   }
   ic <- pmap_dbl(model_opts, compare_ets)
 

tests/testthat/test-ets.R

@@ -164,3 +164,14 @@ test_that("Multiplicative ETS models", {
   )
 })
 
+test_that("Automatic ETS selection bug (#425)", {
+  train <- tsibble(
+    YM = yearmonth("2022 Jan") + 0:35,
+    value = rep(c(rep(-78040, 11), -78061), 3),
+    index = YM
+  )
+  expect_identical(
+    model_sum(model(train, ets=ETS(value))$ets[[1]]),
+    "ETS(A,N,N)"
+  )
+})