Add unit test for extension module with submodule

For portability reasons, this unit test only simulates how an extension
model would look like. It doesn't actually package an extension module,
because then we'd have to provide a separte extension module for each
platform, os, and python version.

pdoc/test/__init__.py

@@ -472,6 +472,35 @@ def test_module(self):
                     self.assertEqual(sorted(m.name for m in m.submodules()),
                                      [EXAMPLE_MODULE + '.' + m for m in submodules])
 
+    @ignore_warnings
+    def test_module_without_path(self):
+        # GH-319: https://github.com/pdoc3/pdoc/issues/319
+        parent_module = ModuleType('parent_module')
+        child_module1 = ModuleType('child_module1')
+        child_module2 = ModuleType('child_module2')
+        grandchild_module = ModuleType('grandchild_module')
+
+        child_module1.grandchild_module = grandchild_module
+        child_module1.__all__ = ['grandchild_module']
+
+        parent_module.child_module1 = child_module1
+        parent_module.child_module2 = child_module2
+        parent_module.__all__ = ['child_module1', 'child_module2']
+
+        assert not hasattr(parent_module, '__path__')
+        assert not hasattr(child_module1, '__path__')
+        assert not hasattr(child_module2, '__path__')
+        assert not hasattr(grandchild_module, '__path__')
+
+        parent_module_pdoc = pdoc.Module(parent_module)
+
+        children_modules_pdoc = sorted(parent_module_pdoc.submodules(), key=lambda m: m.name)
+        self.assertEqual(
+            [m.name for m in children_modules_pdoc], ['child_module1', 'child_module2'])
+        self.assertEqual(
+            [m.name for m in children_modules_pdoc[0].submodules()], ['grandchild_module'])
+        self.assertEqual(children_modules_pdoc[1].submodules(), [])
+
     def test_Module_find_class(self):
         class A:
             pass