tests/cpydiff: Add cpydiff test for __all__ used in imported package.

tests/cpydiff/core_import_all.py

@@ -0,0 +1,9 @@
+"""
+categories: Core,import
+description: __all__ is unsupported in __init__.py in MicroPython.
+cause: Not implemented.
+workaround: Manually import the sub-modules directly in __init__.py using ``from . import foo, bar``.
+"""
+from modules3 import *
+
+foo.hello()

tests/cpydiff/modules3/__init__.py

@@ -0,0 +1 @@
+__all__ = ["foo"]

tests/cpydiff/modules3/foo.py

@@ -0,0 +1,2 @@
+def hello():
+    print("hello")