diff --git a/skimage/util/__init__.py b/skimage/util/__init__.py
index 5577e46b..07712230 100644
--- a/skimage/util/__init__.py
+++ b/skimage/util/__init__.py
@@ -7,6 +7,8 @@ from .arraypad import pad
 from ._regular_grid import regular_grid
 from .unique import unique_rows
 
+from ._warnings import all_warnings
+
 
 __all__ = ['img_as_float',
            'img_as_int',
diff --git a/skimage/util/_warnings.py b/skimage/util/_warnings.py
new file mode 100644
index 00000000..f4bbf5c2
--- /dev/null
+++ b/skimage/util/_warnings.py
@@ -0,0 +1,60 @@
+__all__ = ['all_warnings']
+
+from contextlib import contextmanager
+import sys
+import warnings
+import inspect
+
+@contextmanager
+def all_warnings():
+    """
+    Context for use in testing to ensure that all warnings are raised.
+
+    Examples
+    --------
+    >>> import warnings
+    >>> def foo():
+    ...     warnings.warn(RuntimeWarning("bar"))
+
+    We raise the warning once, while the warning filter is set to "once".
+    Hereafter, the warning is invisible, even with custom filters:
+
+    >>> with warnings.catch_warnings():
+    ...     warnings.simplefilter('once')
+    ...     foo()
+
+    We can now run ``foo()`` without a warning being raised:
+
+    >>> from numpy.testing import assert_warns
+    >>> foo()
+
+    To catch the warning, we call in the help of ``all_warnings``:
+
+    >>> with all_warnings():
+    ...     assert_warns(RuntimeWarning, foo)
+    """
+
+    # Whenever a warning is triggered, Python adds a __warningregistry__
+    # member to the *calling* module.  The exercize here is to find
+    # and eradicate all those breadcrumbs that were left lying around.
+    #
+    # We proceed by first searching all parent calling frames and explicitly
+    # clearing their warning registries (necessary for the doctests above to
+    # pass).  Then, we search for all submodules of skimage and clear theirs
+    # as well (necessary for the skimage test suite to pass).
+
+    frame = inspect.currentframe()
+    if frame:
+        for f in inspect.getouterframes(frame):
+            f[0].f_locals['__warningregistry__'] = {}
+    del frame
+
+    for mod in sys.modules.values():
+        try:
+            mod.__warningregistry__.clear()
+        except AttributeError:
+            pass
+
+    with warnings.catch_warnings():
+        warnings.simplefilter("always")
+        yield