diff --git a/wafo/misc.py b/wafo/misc.py
index 43839d8..fa5cb7f 100644
--- a/wafo/misc.py
+++ b/wafo/misc.py
@@ -3126,13 +3126,6 @@ def fourier(data, t=None, period=None, m=None, n=None, method='trapz'):
     return a, b
 
 
-def test_docstrings():
-    # np.set_printoptions(precision=6)
-    import doctest
-    print('Testing docstrings in %s' % __file__)
-    doctest.testmod(optionflags=doctest.NORMALIZE_WHITESPACE |
-                    doctest.ELLIPSIS)
-
-
 if __name__ == "__main__":
-    test_docstrings()
+    from wafo.testing import test_docstrings
+    test_docstrings(__file__)
diff --git a/wafo/sg_filter/_core.py b/wafo/sg_filter/_core.py
index 7e21ca1..aa4c942 100644
--- a/wafo/sg_filter/_core.py
+++ b/wafo/sg_filter/_core.py
@@ -926,7 +926,8 @@ class Kalman(object):
     def reset(self):
         self._filter = self._filter_first
 
-    def _none_or_atleast_2d(self, a):
+    @staticmethod
+    def _none_or_atleast_2d(a):
         if a is not None:
             return np.atleast_2d(a)
         return a