Avoid fataling on StrictMock(template=str).garbage

Summary:
Accessing nonexistent attributes of `StrictMock`s templated on `str` causes fatals.
This is because of an unfortunate self-reference, where when a `UndefinedAttribute` or `AttributeError` is thrown, it tries to include `f"{self}"`, which invokes `self.__format__`, which hits the attribute handling, which triggers another UndefinedAttribute...

The solution is just to directly point those prints to `repr(self`)`, which works.

Reviewed By: deathowl

Differential Revision: D30966913

fbshipit-source-id: fd84a5ac256b9010acb676a32c6b9b4f8bba7fe0

tests/strict_mock_testslide.py

@@ -814,6 +814,18 @@ def it_yields_the_mock(self):
                                     with self.strict_mock as target:
                                         self.assertTrue(target is self.strict_mock)
 
+            @context.sub_context
+            def string_template(context):
+                @context.example
+                async def undefined_attribute(self) -> None:
+                    with self.assertRaises(UndefinedAttribute):
+                        StrictMock(template=str).join
+
+                @context.example
+                async def attribute_error(self) -> None:
+                    with self.assertRaises(AttributeError):
+                        StrictMock(template=str).garbage
+
             @context.sub_context
             def async_attributes(context):
                 @context.memoize_before

testslide/strict_mock.py

@@ -44,7 +44,7 @@ def __init__(
     def __str__(self) -> str:
         message = (
             f"'{self.name}' is not set.\n"
-            f"{self.strict_mock} must have a value set for this attribute "
+            f"{repr(self.strict_mock)} must have a value set for this attribute "
             "if it is going to be accessed."
         )
         if self.extra_msg is not None:
@@ -767,7 +767,7 @@ def __getattr__(self, name: str) -> Any:
         if self._template and self.__template_has_attr(name):
             raise UndefinedAttribute(self, name)
         else:
-            raise AttributeError(f"'{name}' was not set for {self}.")
+            raise AttributeError(f"'{name}' was not set for {repr(self)}.")
 
     def __delattr__(self, name: str) -> None:
         if name in type(self).__dict__: