cut: add test & improve error message

src/uu/cut/src/cut.rs

@@ -426,7 +426,7 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
                             delim = "";
                         }
                         if delim.chars().count() > 1 {
-                            Err("invalid input: The '--delimiter' ('-d') option expects empty or 1 character long, but was provided a value 2 characters or longer".into())
+                            Err("the delimiter must be a single character".into())
                         } else {
                             let delim = if delim.is_empty() {
                                 "\0".to_owned()

tests/by-util/test_cut.rs

@@ -126,7 +126,7 @@ fn test_too_large() {
 }
 
 #[test]
-fn test_specify_delimiter() {
+fn test_delimiter() {
     for param in ["-d", "--delimiter", "--del"] {
         new_ucmd!()
             .args(&[param, ":", "-f", COMPLEX_SEQUENCE.sequence, INPUT])
@@ -135,6 +135,15 @@ fn test_specify_delimiter() {
     }
 }
 
+#[test]
+fn test_delimiter_with_more_than_one_char() {
+    new_ucmd!()
+        .args(&["-d", "ab", "-f1"])
+        .fails()
+        .stderr_contains("cut: the delimiter must be a single character")
+        .no_stdout();
+}
+
 #[test]
 fn test_output_delimiter() {
     // we use -d here to ensure output delimiter