Add test

Author: AlexWaygood

mypy/test/teststubtest.py

@@ -142,7 +142,10 @@ def test(*args: Any, **kwargs: Any) -> None:
         for c in cases:
             if c.error is None:
                 continue
-            expected_error = "{}.{}".format(TEST_MODULE_NAME, c.error)
+            if c.error:
+                expected_error = "{}.{}".format(TEST_MODULE_NAME, c.error)
+            else:
+                expected_error = TEST_MODULE_NAME
             assert expected_error not in expected_errors, (
                 "collect_cases merges cases into a single stubtest invocation; we already "
                 "expect an error for {}".format(expected_error)
@@ -703,7 +706,12 @@ def h(x: str): ...
             runtime="",
             error="h",
         )
-        yield Case(stub="", runtime="__all__ = []", error=None)  # dummy case
+        # __all__ present at runtime, but not in stub -> error
+        yield Case(stub="", runtime="__all__ = []", error="__all__")
+        # If runtime has __all__ but stub does not,
+        # we should raise an error with the module name itself
+        # if there are any names defined in the stub that are not in the runtime __all__
+        yield Case(stub="_Z = int", runtime="", error="")
         yield Case(stub="", runtime="__all__ += ['y']\ny = 5", error="y")
         yield Case(stub="", runtime="__all__ += ['g']\ndef g(): pass", error="g")
         # Here we should only check that runtime has B, since the stub explicitly re-exports it