Add unit tests for group_contiguous_integers

This module-level utility (used by join_on_conjunctions) had no
direct test coverage of its own, only indirect coverage through
HumanName-level parsing tests. Add focused tests for its documented
contract: empty/isolated/single values return no ranges, adjacent
pairs are the smallest valid run, multiple separate runs are found
independently, and out-of-order input isn't treated as contiguous
(the function assumes ascending, strictly increasing input).

Author: derek73

tests/test_parser_util.py

@@ -0,0 +1,38 @@
+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 function assumes ascending, strictly increasing input (as produced
+    # by an `enumerate`-based index scan, which is how join_on_conjunctions
+    # uses it); descending or out-of-order input won't find real-world runs
+    assert group_contiguous_integers([3, 2, 1]) == []