TEST: Use old-style assert_warns

Author: effigies

nibabel/tests/test_checkwarns.py

@@ -7,8 +7,5 @@ def test_ignore_and_error_warnings():
     with suppress_warnings():
         from .. import checkwarns
 
-    with assert_warns(DeprecationWarning):
-        checkwarns.IgnoreWarnings()
-
-    with assert_warns(DeprecationWarning):
-        checkwarns.ErrorWarnings()
+    assert_warns(DeprecationWarning, checkwarns.IgnoreWarnings)
+    assert_warns(DeprecationWarning, checkwarns.ErrorWarnings)