Add Pep561 tests for stub-only package with namespace packages (#11141)

This only adds tests that show the current behavior when we provide a stub-only package for a subpackage of a namespace package

Proposals for behavior changes exist in python/typeshed#5800

Real world example is the `protobuf` package which installs to `google.protobuf` and the `types-protobuf` package which installs to `google-stubs/protobuf` (where `google` is a namespace package)

Author: nipunn1313

mypy/test/testmodulefinder.py

@@ -184,6 +184,13 @@ def test__packages_with_ns(self) -> None:
             ("ns_pkg_untyped.b.c", ModuleNotFoundReason.FOUND_WITHOUT_TYPE_HINTS),
             ("ns_pkg_untyped.a.a_var", ModuleNotFoundReason.FOUND_WITHOUT_TYPE_HINTS),
 
+            # Namespace package without stub package
+            ("ns_pkg_w_stubs", self.path("ns_pkg_w_stubs")),
+            ("ns_pkg_w_stubs.typed", self.path("ns_pkg_w_stubs-stubs", "typed", "__init__.pyi")),
+            ("ns_pkg_w_stubs.typed_inline",
+                self.path("ns_pkg_w_stubs", "typed_inline", "__init__.py")),
+            ("ns_pkg_w_stubs.untyped", ModuleNotFoundReason.FOUND_WITHOUT_TYPE_HINTS),
+
             # Regular package with py.typed
             ("pkg_typed", self.path("pkg_typed", "__init__.py")),
             ("pkg_typed.a", self.path("pkg_typed", "a.py")),
@@ -239,6 +246,13 @@ def test__packages_without_ns(self) -> None:
             ("ns_pkg_untyped.b.c", ModuleNotFoundReason.FOUND_WITHOUT_TYPE_HINTS),
             ("ns_pkg_untyped.a.a_var", ModuleNotFoundReason.FOUND_WITHOUT_TYPE_HINTS),
 
+            # Namespace package without stub package
+            ("ns_pkg_w_stubs", ModuleNotFoundReason.FOUND_WITHOUT_TYPE_HINTS),
+            ("ns_pkg_w_stubs.typed", ModuleNotFoundReason.FOUND_WITHOUT_TYPE_HINTS),
+            ("ns_pkg_w_stubs.typed_inline",
+                self.path("ns_pkg_w_stubs", "typed_inline", "__init__.py")),
+            ("ns_pkg_w_stubs.untyped", ModuleNotFoundReason.FOUND_WITHOUT_TYPE_HINTS),
+
             # Regular package with py.typed
             ("pkg_typed", self.path("pkg_typed", "__init__.py")),
             ("pkg_typed.a", self.path("pkg_typed", "a.py")),

test-data/packages/typedpkg_ns/typedpkg_ns/ns/__init__.py renamed to test-data/packages/modulefinder-site-packages/ns_pkg_w_stubs-stubs/typed/__init__.pyi

@@ -1,10 +1,10 @@
-from setuptools import setup, find_packages
+from setuptools import setup
 
 setup(
     name='typedpkg_namespace.alpha',
     version='1.0.0',
-    packages=find_packages(),
     namespace_packages=['typedpkg_ns'],
     zip_safe=False,
-    package_data={'typedpkg_ns.ns': ['py.typed']}
+    package_data={'typedpkg_ns.a': ['py.typed']},
+    packages=['typedpkg_ns.a'],
 )