MIL-008: Choose level

Review record RC-041 (Go, autonomous mode, not independent).

Task: MIL-008#1
Task: MIL-008#2
Task: MIL-008#3
Task: MIL-008#4
Task: MIL-008#5
Task: MIL-008#6
Task: MIL-008#7
Task: MIL-008#8

tests/unit/domain/test_level.py

@@ -0,0 +1,42 @@
+"""Tests of the Level value object."""
+
+import dataclasses
+
+import pytest
+
+from flash_card.domain.entities.card import Card
+from flash_card.domain.value_objects.level import Level
+
+CARDS = tuple(Card(f"w{i}", f"v{i}") for i in range(1000))
+
+
+@pytest.mark.parametrize("limit", [0, -1, -100])
+def test_level_refuses_limit_not_above_zero(limit: int) -> None:
+    with pytest.raises(ValueError, match="above zero"):
+        Level(limit)
+
+
+def test_level_accepts_no_limit() -> None:
+    assert Level(None).limit is None
+
+
+def test_level_is_frozen() -> None:
+    level = Level(100)
+    with pytest.raises(dataclasses.FrozenInstanceError):
+        level.limit = 5  # type: ignore[misc]
+
+
+def test_first_returns_first_hundred_cards_when_limit_is_100() -> None:
+    assert Level(100).first(CARDS) == CARDS[:100]
+
+
+def test_first_returns_all_cards_when_there_is_no_limit() -> None:
+    assert Level(None).first(CARDS) == CARDS
+
+
+def test_first_returns_all_cards_when_limit_exceeds_the_list() -> None:
+    assert Level(5000).first(CARDS) == CARDS
+
+
+def test_first_returns_empty_when_list_is_empty() -> None:
+    assert Level(100).first(()) == ()