In general, prefer single quotes

test/02_test/cibuildwheel_test.py

@@ -8,11 +8,11 @@ import utils
 def test():
     # set up the environment
     env = os.environ.copy()
-    env["CIBW_TEST_REQUIRES"] = "nose",
+    env['CIBW_TEST_REQUIRES'] = 'nose',
     # the 'false ||' bit is to ensure this command runs in a shell on
     # mac/linux.
-    env["CIBW_TEST_COMMAND"] = "false || nosetests {project}/test"
-    env["CIBW_TEST_COMMAND_WINDOWS"] = "nosetests {project}/test"
+    env['CIBW_TEST_COMMAND'] = 'false || nosetests {project}/test'
+    env['CIBW_TEST_COMMAND_WINDOWS'] = 'nosetests {project}/test'
 
     # build & test the wheels
     subprocess.check_call([sys.executable, '-m', 'cibuildwheel', project_dir], env=env)