Modify test to close empty file as soon as it's created

Author: Umair Idris

lib/matplotlib/tests/test_backend_bases.py

@@ -78,9 +78,10 @@ def test_get_default_filename_already_exists():
         canvas = FigureCanvasBase(fig)
 
         # create 'image.png' in figure's save dir
-        with open(os.path.join(test_dir, 'image.png'), 'a'):
-            filename = canvas.get_default_filename()
-            assert_equal(filename, 'image-1.png')
+        open(os.path.join(test_dir, 'image.png'), 'w').close()
+
+        filename = canvas.get_default_filename()
+        assert_equal(filename, 'image-1.png')
     finally:
         shutil.rmtree(test_dir)