Remove tests for reencoding unknown encodings

Author: lionel-

tests/testthat/_snaps/c-api.md

@@ -41,10 +41,3 @@
     Output
       <simpleError in r_obj_encode_utf8(c(enc, bytes)): translating strings with "bytes" encoding is not allowed>
 
----
-
-    Code
-      (expect_error(r_obj_encode_utf8(c(enc, bytes))))
-    Output
-      <simpleError in r_obj_encode_utf8(c(enc, bytes)): translating strings with "bytes" encoding is not allowed>
-

tests/testthat/helper-c-api.R

@@ -23,10 +23,18 @@ test_encodings <- function() {
   string <- "\u00B0C"
 
   utf8 <- iconv(string, from = Encoding(string), to = "UTF-8")
-  unknown <- iconv(string, from = Encoding(string), to = "", mark = FALSE)
   latin1 <- iconv(string, from = Encoding(string), to = "latin1")
 
-  list(utf8 = utf8, unknown = unknown, latin1 = latin1)
+  # We used to be able to detect unknown encodings via `LEVELS()`. In recent
+  # versions of R we need to use `Rf_charIsUTF8` instead to be conformant to the
+  # public API but unfortunately it treats unknown encodings as UTF-8. So we
+  # no longer support this case:
+  #
+  # ```
+  # unknown <- iconv(string, from = Encoding(string), to = "", mark = FALSE)
+  # ```
+
+  list(utf8 = utf8, latin1 = latin1)
 }
 expect_utf8_encoded <- function(object) {
   expect_identical(Encoding(object), rep("UTF-8", length(object)))