diff --git a/skimage/filters/tests/test_gaussian.py b/skimage/filters/tests/test_gaussian.py
index 59a0dfaf..14c95d0e 100644
--- a/skimage/filters/tests/test_gaussian.py
+++ b/skimage/filters/tests/test_gaussian.py
@@ -1,21 +1,16 @@
-from nose.tools import raises
 import numpy as np
+from numpy.testing import assert_raises
 from skimage.filters._gaussian import gaussian_filter
 from skimage._shared._warnings import expected_warnings
 
 
-@raises(ValueError)
 def test_negative_sigma():
     a = np.zeros((3, 3))
     a[1, 1] = 1.
-    gaussian_filter(a, -1.0)
-
-
-@raises(ValueError)
-def test_multiple_negative_sigma():
-    a = np.zeros((3, 3))
-    a[1, 1] = 1.
-    gaussian_filter(a, [-1.0, 1.0])
+    assert_raises(ValueError, gaussian_filter, a, sigma=-1.0)
+    assert_raises(ValueError, gaussian_filter, a, sigma=[-1.0, 1.0])
+    assert_raises(ValueError, gaussian_filter, a,
+                  sigma=np.asarray([-1.0, 1.0]))
 
 
 def test_null_sigma():