Prevent persistent temp file creation

pygal/test/test_config.py

@@ -24,6 +24,7 @@ from pygal import (
 from pygal._compat import u
 from pygal.test.utils import texts
 from pygal.test import pytest_generate_tests, make_data
+from tempfile import NamedTemporaryFile
 from uuid import uuid4
 
 
@@ -296,12 +297,12 @@ def test_include_x_axis(Chart):
 
 def test_css(Chart):
     css = "{{ id }}text { fill: #bedead; }\n"
-    css_file = '/tmp/pygal_custom_style-%s.css' % uuid4()
-    with open(css_file, 'w') as f:
+    with NamedTemporaryFile('w') as f:
         f.write(css)
+        f.flush()
 
         config = Config()
-    config.css.append(css_file)
+        config.css.append(f.name)
 
         chart = Chart(config)
         chart.add('/', [10, 1, 5])