fix test_ names

Author: lundybernard

docs/pages/principles/testing.md

@@ -358,7 +358,7 @@ and logical breaks in the path when we transition from the local module
 namespace into an imported dependency's namespace, like so:
 
 ```python
-def test_(mocker):
+def test_func(mocker):
     mock_sum = mocker.patch(
         "project.lib.np.sum"
     )  # you'll need to patch the alias'd namespace
@@ -375,7 +375,7 @@ now you simply need to patch the imported function in the context of the
 file-under-test:
 
 ```python
-def test_(mocker):
+def test_func(mocker):
     np_sum = mocker.patch("project.lib.np_sum")
     ...
 ```