add tests for stub-only package name check

Signed-off-by: Oleg Höfling <oleg.hoefling@gmail.com>

tests/masonry/utils/fixtures/pep_561_stub_only/bad/module.pyi

@@ -0,0 +1,4 @@
+"""Example module"""
+from typing import Tuple
+
+version_info = Tuple[int, int, int]

tests/masonry/utils/fixtures/pep_561_stub_only/good-stubs/module.pyi

@@ -0,0 +1,4 @@
+"""Example module"""
+from typing import Tuple
+
+version_info = Tuple[int, int, int]

tests/masonry/utils/test_package_include.py

@@ -41,3 +41,20 @@ def test_package_include_with_no_python_files_in_dir():
         PackageInclude(base=with_includes, include="not_a_python_pkg")
 
     assert str(e.value) == "not_a_python_pkg is not a package."
+
+
+def test_pep_561_stub_only_package_good_name_suffix():
+    pkg_include = PackageInclude(
+        base=fixtures_dir / "pep_561_stub_only", include="good-stubs"
+    )
+    assert pkg_include.elements == [
+        fixtures_dir / "pep_561_stub_only/good-stubs/__init__.pyi",
+        fixtures_dir / "pep_561_stub_only/good-stubs/module.pyi",
+    ]
+
+
+def test_pep_561_stub_only_package_bad_name_suffix():
+    with pytest.raises(ValueError) as e:
+        PackageInclude(base=fixtures_dir / "pep_561_stub_only", include="bad")
+
+    assert str(e.value) == "bad is not a package."