Skip non-ASCII tests if system does not support UTF-8 (#749)

* fix: skip non-ASCII tests is system does not support UTF-8

* test(exercise_check_unparsable_unicode): split test into one test with a non-ASCII character string and one test with a non-ASCII variable name

* Non-ASCII character strings should work on all platforms
* Non-ASCII variable names should only work on platforms with UTF-8 support

tests/testthat/test-exercise.R

@@ -1222,12 +1222,20 @@ test_that("evaluate_exercise() returns message for unparsable non-ASCII code", {
 
 test_that("evaluate_exercise() does not return a message for parsable non-ASCII code", {
   skip_if_not_pandoc("1.14")
+
+  # Non-ASCII text in character string
+  ex <- mock_exercise(user_code = 'x <- "What\u203d"')
+  result <- evaluate_exercise(ex, new.env())
+  expect_null(result$feedback)
+
   skip_on_os("windows")
+  # Skip if OS does not support UTF-8
+  skip_if(!isTRUE(l10n_info()[["UTF-8"]]))
 
-  # Greek variable name and interrobang in character string
+  # Non-ASCII variable name
   ex <- mock_exercise(
     user_code =
-      '\u03bc\u03b5\u03c4\u03b1\u03b2\u03bb\u03b7\u03c4\u03ae <- "What\u203d"'
+      '\u03bc\u03b5\u03c4\u03b1\u03b2\u03bb\u03b7\u03c4\u03ae <- "What?"'
   )
   result <- evaluate_exercise(ex, new.env())
   expect_null(result$feedback)