feat(test): add mnemonic key derivation tests

Add parameterized tests for generating and deriving keys from mnemonic
sentences. Covers multiple mnemonic sizes, output formats, key types,
and derivation paths. Ensures generated keys exist and match expected
properties.

Author: mkoura

cardano_node_tests/tests/test_mnemonic.py

@@ -0,0 +1,73 @@
+"""Tests for deriving keys from a mnemonic sentence."""
+
+import logging
+import pathlib as pl
+import typing as tp
+
+import allure
+import pytest
+from cardano_clusterlib import clusterlib
+
+from cardano_node_tests.tests import common
+from cardano_node_tests.utils import helpers
+
+LOGGER = logging.getLogger(__name__)
+
+
+@common.SKIPIF_WRONG_ERA
+class TestMnemonic:
+    """Tests for mnemonic sentence."""
+
+    @allure.link(helpers.get_vcs_link())
+    @pytest.mark.parametrize("size", (12, 15, 18, 21, 24))
+    @pytest.mark.parametrize("out", ("file", "stdout"))
+    @pytest.mark.parametrize(
+        "key_type",
+        # pyrefly: ignore  # no-matching-overload
+        iter(clusterlib.KeyType),
+        # pyrefly: ignore  # no-matching-overload
+        ids=(k.value.replace("-", "_") for k in iter(clusterlib.KeyType)),
+    )
+    @pytest.mark.parametrize(
+        "out_format",
+        # pyrefly: ignore  # no-matching-overload
+        iter(clusterlib.OutputFormat),
+        # pyrefly: ignore  # no-matching-overload
+        ids=(k.value.replace("-", "_") for k in iter(clusterlib.OutputFormat)),
+    )
+    @pytest.mark.parametrize("path_num", (0, 2**31 - 1))
+    @pytest.mark.smoke
+    def test_gen_and_deriv(
+        self,
+        cluster: clusterlib.ClusterLib,
+        size: tp.Literal[12, 15, 18, 21, 24],
+        out: str,
+        key_type: clusterlib.KeyType,
+        out_format: clusterlib.OutputFormat,
+        path_num: int,
+    ):
+        """Test `generate-mnemonic` and `derive-from-mnemonic`."""
+        temp_template = common.get_test_id(cluster)
+        mnemonic_file = pl.Path(f"{temp_template}_mnemonic")
+
+        if out == "stdout":
+            words = cluster.g_key.gen_mnemonic(size=size)
+            mnemonic_file.write_text(" ".join(words))
+        else:
+            words = cluster.g_key.gen_mnemonic(size=size, out_file=mnemonic_file)
+        assert len(words) == size
+
+        key_number = (
+            path_num
+            if (key_type in (clusterlib.KeyType.PAYMENT, clusterlib.KeyType.STAKE))
+            else None
+        )
+        key_file = cluster.g_key.derive_from_mnemonic(
+            key_name=f"{temp_template}_derived",
+            key_type=key_type,
+            mnemonic_file=mnemonic_file,
+            account_number=path_num,
+            key_number=key_number,
+            out_format=out_format,
+        )
+        assert key_file.exists()