test(utils): cover lists.first and as_list helpers

tests/_utils/test_lists.py

@@ -0,0 +1,44 @@
+# Copyright 2026 Marimo. All rights reserved.
+from __future__ import annotations
+
+from marimo._utils.lists import as_list, first
+
+
+def test_first_from_list() -> None:
+    assert first([10, 20, 30]) == 10
+
+
+def test_first_from_tuple() -> None:
+    assert first((7,)) == 7
+
+
+def test_first_non_iterable_returns_value() -> None:
+    assert first(42) == 42
+
+
+def test_first_empty_iterable_raises() -> None:
+    raised = False
+    try:
+        first([])
+    except StopIteration:
+        raised = True
+    assert raised
+
+
+def test_first_string_yields_first_character() -> None:
+    # str is Iterable[str]; first returns the first code unit.
+    assert first("abc") == "a"
+
+
+def test_as_list_none() -> None:
+    assert as_list(None) == []
+
+
+def test_as_list_already_list() -> None:
+    value = [1, 2]
+    assert as_list(value) == [1, 2]
+
+
+def test_as_list_scalar() -> None:
+    assert as_list("x") == ["x"]
+    assert as_list(0) == [0]