add autospec to mocker example

Author: lundybernard

docs/pages/principles/testing.md

@@ -360,7 +360,8 @@ namespace into an imported dependency's namespace, like so:
 ```python
 def test_func(mocker):
     mock_sum = mocker.patch(
-        "project.lib.np.sum"
+        "project.lib.np.sum",
+        autospec=True,
     )  # you'll need to patch the alias'd namespace
     ...
 ```
@@ -376,7 +377,7 @@ file-under-test:
 
 ```python
 def test_func(mocker):
-    np_sum = mocker.patch("project.lib.np_sum")
+    np_sum = mocker.patch("project.lib.np_sum", autospec=True)
     ...
 ```