Ensure import of old filter namespace raises warning

skimage/filter/tests/test_filter_import.py

@@ -1,8 +0,0 @@
-from warnings import catch_warnings, simplefilter
-
-def test_import_filter():
-    with catch_warnings():
-        simplefilter('ignore')
-        from skimage import filter as F
-
-    assert('sobel' in dir(F))

skimage/filters/tests/test_filter_import.py

@@ -0,0 +1,11 @@
+from skimage._shared.utils import all_warnings, skimage_deprecation
+from warnings import catch_warnings, simplefilter
+from numpy.testing import assert_warns
+
+def import_filter():
+    from skimage import filter as F
+    assert('sobel' in dir(F))
+
+def test_filter_import():
+    with all_warnings():
+        assert_warns(skimage_deprecation, import_filter)