fix: test_build_default_launches to use an empty package dir

test_build_default_launches was using cibuildwheel setup.cfg which led to the test failing once python 3.6 was dropped.
Use an empty package, provided by fake_package_dir, to run the test.

unit_test/conftest.py

@@ -12,7 +12,7 @@ def pytest_addoption(parser):
 
 
 @pytest.fixture
-def fake_package_dir(monkeypatch):
+def fake_package_dir(tmp_path, monkeypatch):
     """
     Monkey-patch enough for the main() function to run
     """
@@ -25,6 +25,8 @@ def fake_package_dir(monkeypatch):
             return real_path_exists(path)
 
     args = ["cibuildwheel", str(MOCK_PACKAGE_DIR)]
+    tmp_path.joinpath(MOCK_PACKAGE_DIR).mkdir()
     monkeypatch.setattr(Path, "exists", mock_path_exists)
     monkeypatch.setattr(sys, "argv", args)
+    monkeypatch.chdir(tmp_path)
     return args

unit_test/option_prepare_test.py

@@ -44,7 +44,7 @@ def mock_build_container(monkeypatch):
 
 
 def test_build_default_launches(mock_build_container, fake_package_dir, monkeypatch):
-    monkeypatch.setattr(sys, "argv", ["cibuildwheel", "--platform=linux"])
+    monkeypatch.setattr(sys, "argv", sys.argv + ["--platform=linux"])
 
     main()