add test coverage for deep_merge

src/maison/utils.py

@@ -122,6 +122,8 @@ def deep_merge(destination: Dict[Any, Any], source: Dict[Any, Any]) -> Dict[Any,
     ... }
     True
 
+    Note that the arguments may be modified!
+
     Based on https://stackoverflow.com/a/20666342
 
     Args:

tests/unit/test_utils.py

@@ -1,9 +1,18 @@
 """Tests for the `utils` module."""
 from pathlib import Path
+from typing import Any
 from typing import Callable
+from typing import Dict
+from typing import Union
 from unittest.mock import MagicMock
 from unittest.mock import patch
 
+from _pytest.python_api import RaisesContext
+from pytest import mark
+from pytest import param
+from pytest import raises
+
+from maison.utils import deep_merge
 from maison.utils import get_file_path
 from maison.utils import path_contains_file
 
@@ -113,3 +122,44 @@ def test_absolute_path_not_exist(self) -> None:
         result = get_file_path(filename="~/xxxx/yyyy/doesnotexist.xyz")
 
         assert result is None
+
+
+@mark.parametrize(
+    "a,b,expected",
+    [
+        param(
+            {1: 2, 2: 5},
+            {1: 3},
+            {1: 3, 2: 5},
+            id="simple",
+        ),
+        param(
+            {1: {2: 3}, 2: 5},
+            {1: {2: 4}},
+            {1: {2: 4}, 2: 5},
+            id="nested",
+        ),
+        param(
+            {1: 2, 2: 5},
+            {1: {3: 4}},
+            raises(RuntimeError),
+            id="merge-dict-into-scalar",
+        ),
+    ],
+)
+def test_deep_merge(
+    a: Dict[Any, Any],
+    b: Dict[Any, Any],
+    expected: Union[Dict[Any, Any], RaisesContext[Any]],
+) -> None:
+    """
+    Given two dictionaries `a` and `b`,
+    when the `deep_merge` function is invoked with `a` and `b` as arguments,
+    Test that the returned value is as expected.
+    """
+    if isinstance(expected, RaisesContext):
+        with expected:
+            deep_merge(a, b)
+    else:
+        assert deep_merge(a, b) == expected
+        assert a == expected