gh-100690: Raise an AttributeError when the assert_ prefix is forgotten when using Mock (#100691)

Mock objects which are not unsafe will now raise an AttributeError when accessing an
attribute that matches the name of an assertion but without the prefix `assert_`, e.g. accessing `called_once` instead of `assert_called_once`.

This is in addition to this already happening for accessing attributes with prefixes assert, assret, asert, aseert, and assrt.

1 files changed, 10 insertions, 4 deletions

diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index 47928e5..78827d6 100644
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -653,7 +653,7 @@ class NonCallableMock(Base):
         elif _is_magic(name):
             raise AttributeError(name)
         if not self._mock_unsafe and (not self._mock_methods or name not in self._mock_methods):
-            if name.startswith(('assert', 'assret', 'asert', 'aseert', 'assrt')):
+            if name.startswith(('assert', 'assret', 'asert', 'aseert', 'assrt')) or name in ATTRIB_DENY_LIST:
                 raise AttributeError(
                     f"{name!r} is not a valid assertion. Use a spec "
                     f"for the mock if {name!r} is meant to be an attribute.")
@@ -1062,6 +1062,10 @@ class NonCallableMock(Base):
         return f"\n{prefix}: {safe_repr(self.mock_calls)}."
 
 
+# Denylist for forbidden attribute names in safe mode
+ATTRIB_DENY_LIST = {name.removeprefix("assert_") for name in dir(NonCallableMock) if name.startswith("assert_")}
+
+
 class _AnyComparer(list):
     """A list which checks if it contains a call which may have an
     argument of ANY, flipping the components of item and self from
@@ -1231,9 +1235,11 @@ class Mock(CallableMixin, NonCallableMock):
       `return_value` attribute.
 
     * `unsafe`: By default, accessing any attribute whose name starts with
-      *assert*, *assret*, *asert*, *aseert* or *assrt* will raise an
-       AttributeError. Passing `unsafe=True` will allow access to
-      these attributes.
+      *assert*, *assret*, *asert*, *aseert*, or *assrt* raises an AttributeError.
+      Additionally, an AttributeError is raised when accessing
+      attributes that match the name of an assertion method without the prefix
+      `assert_`, e.g. accessing `called_once` instead of `assert_called_once`.
+      Passing `unsafe=True` will allow access to these attributes.
 
     * `wraps`: Item for the mock object to wrap. If `wraps` is not None then
       calling the Mock will pass the call through to the wrapped object