From ff4e3bd0bd810099eb7da3bc9c707cedc5997f59 Mon Sep 17 00:00:00 2001
From: John Wiggins <jwiggins@enthought.com>
Date: Fri, 28 Aug 2015 20:37:26 +0200
Subject: [PATCH 1/4] Raise an error for negative sigma values in
 guassian_filter.

---
 skimage/filters/_gaussian.py | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/skimage/filters/_gaussian.py b/skimage/filters/_gaussian.py
index 6bc12574..a02b6bdb 100644
--- a/skimage/filters/_gaussian.py
+++ b/skimage/filters/_gaussian.py
@@ -74,6 +74,10 @@ def gaussian_filter(image, sigma, output=None, mode='nearest', cval=0,
     array([[ 0.05855018,  0.09653293,  0.05855018],
            [ 0.09653293,  0.15915589,  0.09653293],
            [ 0.05855018,  0.09653293,  0.05855018]])
+    >>> gaussian_filter(a, sigma=-1)
+    Traceback (most recent call last):
+    ...
+    ValueError: Sigma values less than zero are not valid
     >>> # Several modes are possible for handling boundaries
     >>> gaussian_filter(a, sigma=1, mode='reflect')
     array([[ 0.08767308,  0.12075024,  0.08767308],
@@ -93,6 +97,9 @@ def gaussian_filter(image, sigma, output=None, mode='nearest', cval=0,
                "3D image with last dimension of length 3.")
         warnings.warn(RuntimeWarning(msg))
         multichannel = True
+    if np.any(np.asarray(sigma) < 0.0):
+        msg = "Sigma values less than zero are not valid"
+        raise ValueError(msg)
     if multichannel:
         # do not filter across channels
         if not isinstance(sigma, coll.Iterable):

From c05108da3687bf6854bf391e1d84add5c0062141 Mon Sep 17 00:00:00 2001
From: John Wiggins <jwiggins@enthought.com>
Date: Fri, 28 Aug 2015 21:03:01 +0200
Subject: [PATCH 2/4] Replace a doc test with some regular unit tests.

---
 skimage/filters/_gaussian.py           |  4 ----
 skimage/filters/tests/test_gaussian.py | 15 +++++++++++++++
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/skimage/filters/_gaussian.py b/skimage/filters/_gaussian.py
index a02b6bdb..643dca05 100644
--- a/skimage/filters/_gaussian.py
+++ b/skimage/filters/_gaussian.py
@@ -74,10 +74,6 @@ def gaussian_filter(image, sigma, output=None, mode='nearest', cval=0,
     array([[ 0.05855018,  0.09653293,  0.05855018],
            [ 0.09653293,  0.15915589,  0.09653293],
            [ 0.05855018,  0.09653293,  0.05855018]])
-    >>> gaussian_filter(a, sigma=-1)
-    Traceback (most recent call last):
-    ...
-    ValueError: Sigma values less than zero are not valid
     >>> # Several modes are possible for handling boundaries
     >>> gaussian_filter(a, sigma=1, mode='reflect')
     array([[ 0.08767308,  0.12075024,  0.08767308],
diff --git a/skimage/filters/tests/test_gaussian.py b/skimage/filters/tests/test_gaussian.py
index c88ee1f8..59a0dfaf 100644
--- a/skimage/filters/tests/test_gaussian.py
+++ b/skimage/filters/tests/test_gaussian.py
@@ -1,8 +1,23 @@
+from nose.tools import raises
 import numpy as np
 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])
+
+
 def test_null_sigma():
     a = np.zeros((3, 3))
     a[1, 1] = 1.

From a0fc75c7cb335264f46ee1a88f83624734dc4bfe Mon Sep 17 00:00:00 2001
From: John Wiggins <jwiggins@enthought.com>
Date: Fri, 28 Aug 2015 21:10:39 +0200
Subject: [PATCH 3/4] Don't use two lines to raise an exception with a short
 message.

---
 skimage/filters/_gaussian.py | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/skimage/filters/_gaussian.py b/skimage/filters/_gaussian.py
index 643dca05..85b572ca 100644
--- a/skimage/filters/_gaussian.py
+++ b/skimage/filters/_gaussian.py
@@ -94,8 +94,7 @@ def gaussian_filter(image, sigma, output=None, mode='nearest', cval=0,
         warnings.warn(RuntimeWarning(msg))
         multichannel = True
     if np.any(np.asarray(sigma) < 0.0):
-        msg = "Sigma values less than zero are not valid"
-        raise ValueError(msg)
+        raise ValueError("Sigma values less than zero are not valid")
     if multichannel:
         # do not filter across channels
         if not isinstance(sigma, coll.Iterable):

From 6e6d243dbdb91c70bb3cd26567e9ee877e245d23 Mon Sep 17 00:00:00 2001
From: John Wiggins <jwiggins@enthought.com>
Date: Fri, 28 Aug 2015 21:19:20 +0200
Subject: [PATCH 4/4] Use assert_raises instead of @raises.

---
 skimage/filters/tests/test_gaussian.py | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

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():