cut: split test function into two functions

tests/by-util/test_cut.rs

@@ -212,7 +212,7 @@ fn test_zero_terminated_only_delimited() {
 }
 
 #[test]
-fn test_directory_and_no_such_file() {
+fn test_is_a_directory() {
     let (at, mut ucmd) = at_and_ucmd!();
 
     at.mkdir("some");
@@ -221,7 +221,10 @@ fn test_directory_and_no_such_file() {
         .arg("some")
         .run()
         .stderr_is("cut: some: Is a directory\n");
+}
 
+#[test]
+fn test_no_such_file() {
     new_ucmd!()
         .arg("-b1")
         .arg("some")