More rigorous tests for dynamic file location.

tests/test_thirdparty.py

@@ -10,16 +10,30 @@
 
 def test_module_paths():
     "Third party binary modules have meaningful __file__ attributes"
+    import decimal
+
+    import _decimal
+    import lru
     import PIL
     from PIL import _imaging
 
     # iOS and Android both play shenanigans with binary locations.
     # Make sure the __file__ attribute on the binary module reflects
-    # the actual location in the file system. The base PIL module is
-    # pure Python; the binary module for PIL._imaging should be in
-    # the same folder.
+    # the actual location in the file system.
+    # decimal is in the standard library; it is backed by a binary module in the
+    # lib-dynload folder.
+    assert (
+        Path(_decimal.__file__).parent == Path(decimal.__file__).parent / "lib-dynload"
+    )
+
+    # The base PIL module is an __init__.py that is pure Python; the binary module for
+    # PIL._imaging should be in the same folder.
     assert Path(_imaging.__file__).parent == Path(PIL.__file__).parent
 
+    # lru is an extension module that is at the root of the app_packages folder.
+    # The app_packages folder is the one that holds PIL.
+    assert Path(lru.__file__).parent == Path(PIL.__file__).parent.parent
+
 
 @pytest.mark.skipif(sys.platform == "win32", reason="cffi not available on windows")
 def test_cffi():