tests: include some additional tests and docs

Author: michaelbrewer

aws_lambda_powertools/utilities/parameters/base.py

@@ -163,7 +163,34 @@ def _get_multiple(self, path: str, **sdk_options) -> Dict[str, str]:
         raise NotImplementedError()
 
 
-def get_transform_method(key: str, transform: str) -> Union[str, None]:
+def get_transform_method(key: str, transform: str) -> Optional[str]:
+    """
+    Determine the transform method
+
+    Examples
+    -------
+        >>> get_transform_method("key", "any_other_value")
+        'any_other_value'
+        >>> get_transform_method("key.json", "auto")
+        'json'
+        >>> get_transform_method("key.binary", "auto")
+        'binary'
+        >>> get_transform_method("key", "auto")
+        None
+
+    Parameters
+    ---------
+    key: str
+        Only used when the tranform is "auto".
+    transform: str
+        Original transform method, only "auto" will try to detect the transform method by the key
+
+    Returns
+    ------
+    Optional[str]:
+        The transform method either when transform is "auto" then None, "json" or "binary" is returned
+        or the original transform method
+    """
     if transform != "auto":
         return transform
 

tests/functional/test_utilities_parameters.py

@@ -1523,3 +1523,34 @@ def test_transform_value_ignore_error(mock_value):
     value = parameters.base.transform_value(mock_value, "INCORRECT", raise_on_transform_error=False)
 
     assert value is None
+
+
+@pytest.mark.parametrize("original_transform", ["json", "binary", "other", "Auto"])
+def test_get_transform_method_preserve_original(original_transform):
+    """
+    Check if original transform method is returned for anything other than "auto"
+    """
+    transform = parameters.base.get_transform_method("key", original_transform)
+
+    assert transform == original_transform
+
+
+@pytest.mark.parametrize("extension", ["json", "binary"])
+def test_get_transform_method_preserve_auto(extension, mock_name):
+    """
+    Check if we can auto detect the transform method by the support extensions json / binary
+    """
+    transform = parameters.base.get_transform_method(f"{mock_name}.{extension}", "auto")
+
+    assert transform == extension
+
+
+@pytest.mark.parametrize("key", ["json", "binary", "example", "example.jsonp"])
+def test_get_transform_method_preserve_auto_unhandled(key):
+    """
+    Check if any key that does not end with a supported extension returns None when
+    using the transform="auto"
+    """
+    transform = parameters.base.get_transform_method(key, "auto")
+
+    assert transform is None