Add tests to check link fails with 1 or 3 argument(s)

tests/by-util/test_link.rs

@@ -39,3 +39,25 @@ fn test_link_nonexistent_file() {
     assert!(!at.file_exists(file));
     assert!(!at.file_exists(link));
 }
+
+#[test]
+fn test_link_one_argument() {
+    let (_, mut ucmd) = at_and_ucmd!();
+    let file = "test_link_argument";
+    ucmd.args(&[file]).fails().stderr_contains(
+        "error: The argument '<FILES>...' requires at least 2 values, but only 1 was provide",
+    );
+}
+
+#[test]
+fn test_link_three_arguments() {
+    let (_, mut ucmd) = at_and_ucmd!();
+    let arguments = vec![
+        "test_link_argument1",
+        "test_link_argument2",
+        "test_link_argument3",
+    ];
+    ucmd.args(&arguments[..]).fails().stderr_contains(
+        format!("error: The value '{}' was provided to '<FILES>...', but it wasn't expecting any more values", arguments[2]),
+    );
+}