error: Unknown word: concat
 --> tests/ui/bad_concat.rs:5:9
  |
5 |         concat,
  |         ^^^^^^

error: unexpected end of input, Concat must have at least two elements
 --> tests/ui/bad_concat.rs:8:16
  |
8 |         concat(),
  |                ^

error: unexpected end of input, Concat must have at least two elements
  --> tests/ui/bad_concat.rs:11:21
   |
11 |         concat("one"),
   |                     ^

error: regex parse error:
           [
           ^
       error: unclosed character class
  --> tests/ui/bad_concat.rs:14:22
   |
14 |         concat(regex("["), "two"),
   |                      ^^^