Assert that warning is raised

Author: radarhere

Tests/test_imagefile.py

@@ -95,8 +95,9 @@ def test_safeblock(self):
 
     def test_raise_ioerror(self):
         with pytest.raises(IOError):
-            with pytest.warns(DeprecationWarning):
+            with pytest.warns(DeprecationWarning) as record:
                 ImageFile.raise_ioerror(1)
+        assert len(record) == 1
 
     def test_raise_oserror(self):
         with pytest.raises(OSError):