Add test and amend docstrings

src/ytdl_sub/cli/download_args_parser.py

@@ -88,7 +88,7 @@ class DownloadArgsParser:
         :param indices: List of indices
         :return: Largest integer n + 1 so that all the integers from 0 up to n exist
                  in the indices.
-                 -1 if indices list is empty or the smallest integer in indices is larger that 0.
+                 0 if indices list is empty or the smallest integer in indices is larger than 0.
         """
         largest_consecutive = -1
         indices.sort()

tests/unit/cli/test_download_args_parser.py

@@ -86,6 +86,11 @@ class TestDownloadArgsParser:
                 "dl --parameter.using.list[2] 'v3' --parameter.using.list[1] 'v1' --parameter.using.list[2] 'v2'",
                 {"parameter": {"using": {"list": ["v1", "v2"]}}},
             ),
+            (
+                None,
+                "dl --parameter.using.list[3] 'v3' --parameter.using.list[1] 'v1'",
+                {"parameter": {"using": {"list": ["v1"]}}},
+            ),
             (
                 None,
                 "dl --parameter.not.using.list[0] 'v0'",