diff --git a/tests/test_parser_util.py b/tests/test_parser_util.py
new file mode 100644
index 0000000..a2b74f5
--- /dev/null
+++ b/tests/test_parser_util.py
@@ -0,0 +1,39 @@
+from nameparser.parser import group_contiguous_integers
+
+
+def test_empty_list_returns_no_ranges() -> None:
+    assert group_contiguous_integers([]) == []
+
+
+def test_all_isolated_values_returns_no_ranges() -> None:
+    # no two values are adjacent, so nothing counts as a "run"
+    assert group_contiguous_integers([1, 3, 5]) == []
+
+
+def test_single_value_returns_no_ranges() -> None:
+    # a run of length 1 isn't a contiguous "run" by this function's definition
+    assert group_contiguous_integers([5]) == []
+
+
+def test_pair_of_adjacent_values_is_smallest_valid_run() -> None:
+    assert group_contiguous_integers([4, 5]) == [(4, 5)]
+
+
+def test_single_contiguous_run() -> None:
+    assert group_contiguous_integers([1, 2, 3]) == [(1, 3)]
+
+
+def test_multiple_separate_contiguous_runs() -> None:
+    assert group_contiguous_integers([1, 2, 5, 6, 7, 9]) == [(1, 2), (5, 7)]
+
+
+def test_isolated_values_between_runs_are_excluded() -> None:
+    assert group_contiguous_integers([1, 2, 4, 6, 7]) == [(1, 2), (6, 7)]
+
+
+def test_unsorted_input_is_not_treated_as_contiguous() -> None:
+    # the grouping key (enumerate index - value) only repeats for ascending,
+    # strictly increasing runs (as produced by an `enumerate`-based index
+    # scan, which is how join_on_conjunctions uses it); a descending
+    # sequence changes the key at every step, so no run is ever found
+    assert group_contiguous_integers([3, 2, 1]) == []