MIL-003: Step 2 - New flash cards

Review record RC-025 (Go, autonomous mode, not independent).

Task: MIL-003#1
Task: MIL-003#2
Task: MIL-003#3
Task: MIL-003#4
Task: MIL-003#5

tests/unit/domain/test_card.py

@@ -0,0 +1,38 @@
+"""Tests of the Card, LanguagePair and Vocabulary value types."""
+
+import dataclasses
+
+import pytest
+
+from flash_card.domain.entities.card import Card
+from flash_card.domain.entities.vocabulary import Vocabulary
+from flash_card.domain.value_objects.language_pair import LanguagePair
+
+
+def test_card_equals_card_with_same_texts() -> None:
+    assert Card("aku", "mig") == Card("aku", "mig")
+
+
+def test_card_is_frozen() -> None:
+    card = Card("aku", "mig")
+    with pytest.raises(dataclasses.FrozenInstanceError):
+        card.front = "kau"  # type: ignore[misc]
+
+
+def test_language_pair_holds_codes() -> None:
+    pair = LanguagePair("ms", "da")
+    assert (pair.front_code, pair.back_code) == ("ms", "da")
+
+
+def test_language_pair_is_frozen() -> None:
+    pair = LanguagePair("ms", "da")
+    with pytest.raises(dataclasses.FrozenInstanceError):
+        pair.front_code = "en"  # type: ignore[misc]
+
+
+def test_vocabulary_holds_pair_and_cards() -> None:
+    pair = LanguagePair("ms", "da")
+    cards = (Card("aku", "mig"),)
+    vocabulary = Vocabulary(pair, cards)
+    assert vocabulary.language_pair == pair
+    assert vocabulary.cards == cards