diff --git a/pyproject.toml b/pyproject.toml
index 18fcd0e..8677108 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -76,7 +76,7 @@ filterwarnings = [
 ]
 log_cli_level = "INFO"
 testpaths = [
-  "tests",
+  "src", "tests",
 ]
 
 
diff --git a/src/dataclasstools/_ext.py b/src/dataclasstools/_ext.py
index 344cdcf..8c69e19 100644
--- a/src/dataclasstools/_ext.py
+++ b/src/dataclasstools/_ext.py
@@ -2,7 +2,7 @@
 
 __all__ = ["field_keys", "field_values", "field_items"]
 
-from collections.abc import Hashable, Iterator, Mapping
+from collections.abc import Hashable, ItemsView, Iterator, KeysView, Mapping, ValuesView
 from typing import Any, TypeVar
 
 from plum import dispatch
@@ -40,7 +40,7 @@ def field_keys(obj: Any, /) -> Iterator[str]:
 
 @dispatch  # type: ignore[no-redef]
 # TODO: def field_keys(obj: Mapping[K, V]) -> Iterator[K]:
-def field_keys(obj: Mapping[Hashable, Any]) -> Iterator[Hashable]:
+def field_keys(obj: Mapping[Hashable, Any]) -> KeysView[Hashable]:
     """Return the keys of a mapping.
 
     Examples
@@ -48,11 +48,11 @@ def field_keys(obj: Mapping[Hashable, Any]) -> Iterator[Hashable]:
     >>> from dataclasstools import field_keys
 
     >>> p = {"a": 1, "b": 2.0, "c": "3"}
-    >>> list(field_keys(p))
-    ['a', 'b', 'c']
+    >>> field_keys(p)
+    dict_keys(['a', 'b', 'c'])
 
     """
-    yield from obj.keys()
+    return obj.keys()
 
 
 # ===================================================================
@@ -83,7 +83,7 @@ def field_values(obj: Any, /) -> Iterator[Any]:
 
 @dispatch  # type: ignore[no-redef]
 # TODO: def field_values(obj: Mapping[Any, V]) -> Iterator[V]:
-def field_values(obj: Mapping[Any, Any]) -> Iterator[Any]:
+def field_values(obj: Mapping[Any, Any]) -> ValuesView[Any]:
     """Return the values of a mapping.
 
     Examples
@@ -91,11 +91,11 @@ def field_values(obj: Mapping[Any, Any]) -> Iterator[Any]:
     >>> from dataclasstools import field_values
 
     >>> p = {"a": 1, "b": 2.0, "c": "3"}
-    >>> list(field_values(p))
-    [1, 2.0, '3']
+    >>> field_values(p)
+    dict_values([1, 2.0, '3'])
 
     """
-    yield from obj.values()
+    return obj.values()
 
 
 # ===================================================================
@@ -126,7 +126,7 @@ def field_items(obj: Any) -> Iterator[tuple[str, Any]]:
 
 @dispatch  # type: ignore[no-redef]
 # TODO: def field_items(obj: Mapping[K, V]) -> Iterator[tuple[K, V]]:
-def field_items(obj: Mapping[Any, Any]) -> Iterator[tuple[Any, Any]]:
+def field_items(obj: Mapping[Any, Any]) -> ItemsView[Any, Any]:
     """Return the items of a mapping.
 
     Examples
@@ -134,8 +134,8 @@ def field_items(obj: Mapping[Any, Any]) -> Iterator[tuple[Any, Any]]:
     >>> from dataclasstools import field_items
 
     >>> p = {"a": 1, "b": 2.0, "c": "3"}
-    >>> list(field_items(p))
-    [('a', 1), ('b', 2.0), ('c', '3')]
+    >>> field_items(p)
+    dict_items([('a', 1), ('b', 2.0), ('c', '3')])
 
     """
-    yield from obj.items()
+    return obj.items()