Require at least 2 PIT values for boundary correction

Author: jgabry

R/ppc-loo.R

@@ -303,6 +303,9 @@ ppc_loo_pit_data <-
            grid_len = 512) {
     if (!is.null(pit)) {
       pit <- validate_pit(pit)
+      if (boundary_correction && length(pit) < 2L) {
+        abort("At least 2 PIT values are required when 'boundary_correction' is TRUE.")
+      }
       inform("'pit' specified so ignoring 'y','yrep','lw' if specified.")
     } else {
       suggested_package("rstantools")

tests/testthat/test-ppc-loo.R

@@ -76,6 +76,14 @@ test_that("ppc_loo_pit_data validates user-provided pit values", {
     ppc_loo_pit_data(pit = "not numeric"),
     "is.numeric"
   )
+  expect_error(
+    ppc_loo_pit_data(pit = c(Inf, -Inf, Inf)),
+    "between 0 and 1"
+  )
+  expect_error(
+    ppc_loo_pit_data(pit = 0.5, boundary_correction = TRUE),
+    "At least 2 PIT values"
+  )
 })
 
 test_that("ppc_loo_pit_qq validates user-provided pit values", {