Proper loading for third-party stub packages

test/examples/stub_packages/no_python-stubs/__init__.pyi

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+foo: int

test/examples/stub_packages/with_python-stubs/__init__.pyi

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+both: int
+stub_only: str

test/examples/stub_packages/with_python-stubs/module.pyi

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+in_sub_module: int

test/examples/stub_packages/with_python/__init__.py

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+python_only = 1
+both = ''

test/examples/stub_packages/with_python/module.py

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+in_sub_module = ''

test/test_evaluate/test_gradual/test_stub_loading.py

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+from functools import partial
+from test.helpers import get_example_dir
+from jedi.api.project import Project
+
+import pytest
+
+
+@pytest.fixture
+def ScriptInStubFolder(Script):
+    path = get_example_dir('stub_packages')
+    project = Project(path, sys_path=[path], smart_sys_path=False)
+    return partial(Script, _project=project)
+
+
+@pytest.mark.parametrize(
+    ('code', 'expected'), [
+        ('from no_python import foo', ['int']),
+        ('from with_python import stub_only', ['str']),
+        ('from with_python import python_only', []),
+        ('from with_python import both', ['int']),
+        ('from with_python import something_random', []),
+        ('from with_python.module import in_sub_module', ['int']),
+    ]
+)
+def test_find_stubs_infer(ScriptInStubFolder, code, expected):
+    defs = ScriptInStubFolder(code).goto_definitions()
+    assert [d.name for d in defs] == expected