Run each test using a temporary directory (#217)

test/04_build_skip/cibuildwheel_test.py

@@ -5,7 +5,7 @@ def test():
     project_dir = os.path.dirname(__file__)
 
     # build the wheels
-    utils.cibuildwheel_run(project_dir, add_env={
+    actual_wheels = utils.cibuildwheel_run(project_dir, add_env={
         'CIBW_BUILD': 'cp3?-*',
         'CIBW_SKIP': 'cp37-*',
     })
@@ -13,5 +13,4 @@ def test():
     # check that we got the right wheels. There should be no 2.7 or 3.7.
     expected_wheels = [w for w in utils.expected_wheels('spam', '0.1.0')
                        if ('-cp3' in w) and ('-cp37' not in w)]
-    actual_wheels = os.listdir('wheelhouse')
     assert set(actual_wheels) == set(expected_wheels)