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_vocabulary_errors.py

@@ -0,0 +1,21 @@
+"""Tests of the vocabulary error hierarchy."""
+
+import pytest
+
+from flash_card.domain.errors.vocabulary_errors import (
+    EmptyDeckError,
+    VocabularyError,
+    VocabularyFormatError,
+    VocabularyNotFoundError,
+)
+
+
+@pytest.mark.parametrize(
+    "error", [VocabularyFormatError, VocabularyNotFoundError, EmptyDeckError]
+)
+def test_error_is_a_vocabulary_error(error: type[VocabularyError]) -> None:
+    assert issubclass(error, VocabularyError)
+
+
+def test_vocabulary_error_is_an_exception() -> None:
+    assert issubclass(VocabularyError, Exception)