refactor: Override options redesign

* Add test for defaults, fix platform detection

* Improve correctness of reader.identifier with block

* Fix options test to be multiplatform

* 'Refactored by Sourcery'

docs: write a section on overrides

tests: test docker launches

feat: add identifiers to launches

test: add test for correct build step generation

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

unit_test/conftest.py

@@ -1,5 +1,10 @@
+import sys
+from pathlib import Path
+
 import pytest
 
+MOCK_PACKAGE_DIR = Path("some_package_dir")
+
 
 def pytest_addoption(parser):
     parser.addoption("--run-docker", action="store_true", default=False, help="run docker tests")
@@ -17,3 +22,22 @@ def pytest_collection_modifyitems(config, items):
     for item in items:
         if "docker" in item.keywords:
             item.add_marker(skip_docker)
+
+
+@pytest.fixture
+def fake_package_dir(monkeypatch):
+    """
+    Monkey-patch enough for the main() function to run
+    """
+    real_path_exists = Path.exists
+
+    def mock_path_exists(path):
+        if path == MOCK_PACKAGE_DIR / "setup.py":
+            return True
+        else:
+            return real_path_exists(path)
+
+    args = ["cibuildwheel", str(MOCK_PACKAGE_DIR)]
+    monkeypatch.setattr(Path, "exists", mock_path_exists)
+    monkeypatch.setattr(sys, "argv", args)
+    return args