tests: add unit tests for dict_filter

tests/unit/utils/test_dict_filter.py

@@ -0,0 +1,30 @@
+from dvc.utils import dict_filter
+
+
+def test_flat_exclusion():
+    assert dict_filter({"a": 1, "b": 2}, exclude=["b"]) == {"a": 1}
+
+
+def test_multiple_excludes():
+    assert dict_filter({"a": 1, "b": 2, "c": 3}, exclude=["a", "c"]) == {"b": 2}
+
+
+def test_nested_key_removed_recursively():
+    assert dict_filter({"a": {"b": 2, "c": 3}}, exclude=["b"]) == {"a": {"c": 3}}
+
+
+def test_excluded_key_removes_its_subtree():
+    assert dict_filter({"a": 1, "b": {"x": 1}}, exclude=["b"]) == {"a": 1}
+
+
+def test_list_of_dicts_is_filtered_elementwise():
+    result = dict_filter([{"b": 1, "a": 2}, {"a": 3}], exclude=["b"])
+    assert result == [{"a": 2}, {"a": 3}]
+
+
+def test_no_exclude_returns_input_unchanged():
+    assert dict_filter({"a": 1}) == {"a": 1}
+
+
+def test_scalar_is_passed_through():
+    assert dict_filter(5, exclude=["b"]) == 5