Correct handling of test_sources on universal macOS builds. (#2284)

* Correct handling of test_sources on universal macOS builds.

* Make the test sources modifications macOS only.

* Don't use unittest discovery - that needs an actual test.

* Add comment explaining test source creation

Co-authored-by: Joe Rickerby <joerick@mac.com>

* Simplify dict usage.

---------

Co-authored-by: Joe Rickerby <joerick@mac.com>

cibuildwheel/macos.py

@@ -717,12 +717,15 @@ def build(options: Options, tmp_path: Path) -> None:
 
                     if build_options.test_sources:
                         test_cwd = identifier_tmp_dir / "test_cwd"
-                        test_cwd.mkdir(exist_ok=True)
-                        copy_test_sources(
-                            build_options.test_sources,
-                            build_options.package_dir,
-                            test_cwd,
-                        )
+                        # only create test_cwd if it doesn't already exist - it
+                        # may have been created during a previous `testing_arch`
+                        if not test_cwd.exists():
+                            test_cwd.mkdir()
+                            copy_test_sources(
+                                build_options.test_sources,
+                                build_options.package_dir,
+                                test_cwd,
+                            )
                     else:
                         # There are no test sources. Run the tests in the project directory.
                         test_cwd = Path(".").resolve()

test/test_macos_archs.py

@@ -8,6 +8,11 @@ import pytest
 from . import test_projects, utils
 
 basic_project = test_projects.new_c_project()
+basic_project.files["tests/test_suite.py"] = r"""
+import platform
+print("running tests on " + platform.machine())
+"""
+
 
 ALL_MACOS_WHEELS = {
     *utils.expected_wheels("spam", "0.1.0", machine_arch="x86_64"),
@@ -51,7 +56,21 @@ def test_cross_compiled_build(tmp_path):
 
 
 @pytest.mark.parametrize("build_universal2", [False, True])
-def test_cross_compiled_test(tmp_path, capfd, build_universal2):
+@pytest.mark.parametrize(
+    "test_config",
+    [
+        # Run the test suite in the project folder
+        {
+            "CIBW_TEST_COMMAND": '''python -c "import platform; print('running tests on ' + platform.machine())"''',
+        },
+        # Nominate the set of test sources to copy
+        {
+            "CIBW_TEST_COMMAND": "python tests/test_suite.py",
+            "CIBW_TEST_SOURCES": "tests",
+        },
+    ],
+)
+def test_cross_compiled_test(tmp_path, capfd, build_universal2, test_config):
     if utils.platform != "macos":
         pytest.skip("this test is only relevant to macos")
     if get_xcode_version() < (12, 2):
@@ -64,9 +83,9 @@ def test_cross_compiled_test(tmp_path, capfd, build_universal2):
         project_dir,
         add_env={
             "CIBW_BUILD": "cp310-*" if build_universal2 else "*p310-*",
-            "CIBW_TEST_COMMAND": '''python -c "import platform; print('running tests on ' + platform.machine())"''',
             "CIBW_ARCHS": "universal2" if build_universal2 else "x86_64 arm64",
             "CIBW_BUILD_VERBOSITY": "3",
+            **test_config,
         },
     )