From 574159f724fe2acf324b5e29d98743b29b9e4f65 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Johannes=20Sch=C3=B6nberger?= <jsch@demuc.de>
Date: Tue, 19 May 2015 17:57:47 -0700
Subject: [PATCH 1/2] Add decorator to test parallel execution of unit test

---
 skimage/_shared/testing.py            | 33 +++++++++++++++++++++++++++
 skimage/transform/tests/test_warps.py |  2 +-
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/skimage/_shared/testing.py b/skimage/_shared/testing.py
index f202fbff..5069e19e 100644
--- a/skimage/_shared/testing.py
+++ b/skimage/_shared/testing.py
@@ -3,6 +3,8 @@
 
 import os
 import re
+import threading
+import functools
 from tempfile import NamedTemporaryFile
 
 from numpy import testing
@@ -201,6 +203,37 @@ def teardown_test():
     warnings.simplefilter('default')
 
 
+def test_parallel(num_threads=2):
+    """Decorator to run the same function multiple times in parallel.
+
+    Parameters
+    ----------
+    num_threads : int, optional
+        The number of times the function is run in parallel.
+
+    Notes
+    -----
+    This decorator does not pass the return value of the decorated function.
+
+    """
+
+    assert num_threads > 0
+
+    def wrapper(func):
+        @functools.wraps(func)
+        def inner(*args, **kwargs):
+            threads = []
+            for i in range(num_threads):
+                thread = threading.Thread(target=func, args=args, kwargs=kwargs)
+                threads.append(thread)
+            for thread in threads:
+                thread.start()
+            for thread in threads:
+                thread.join()
+        return inner
+    return wrapper
+
+
 if __name__ == '__main__':
     color_check('pil')
     mono_check('pil')
diff --git a/skimage/transform/tests/test_warps.py b/skimage/transform/tests/test_warps.py
index 115f0e6f..afa78da3 100644
--- a/skimage/transform/tests/test_warps.py
+++ b/skimage/transform/tests/test_warps.py
@@ -197,7 +197,7 @@ def test_swirl():
     image = img_as_float(data.checkerboard())
 
     swirl_params = {'radius': 80, 'rotation': 0, 'order': 2, 'mode': 'reflect'}
-    
+
     with expected_warnings(['Bi-quadratic.*bug']):
         swirled = tf.swirl(image, strength=10, **swirl_params)
         unswirled = tf.swirl(swirled, strength=-10, **swirl_params)

From 0fad295d471061bda13ebcfaf925a381d6aeb386 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Johannes=20Sch=C3=B6nberger?= <jsch@demuc.de>
Date: Tue, 19 May 2015 18:15:17 -0700
Subject: [PATCH 2/2] Add unit test for test_parallel decorator

---
 skimage/_shared/tests/test_testing.py | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/skimage/_shared/tests/test_testing.py b/skimage/_shared/tests/test_testing.py
index a8b662bb..0ad15942 100644
--- a/skimage/_shared/tests/test_testing.py
+++ b/skimage/_shared/tests/test_testing.py
@@ -3,7 +3,7 @@
 
 import numpy as np
 from nose.tools import (assert_true, assert_raises, assert_equal)
-from skimage._shared.testing import doctest_skip_parser
+from skimage._shared.testing import doctest_skip_parser, test_parallel
 
 
 def test_skipper():
@@ -84,5 +84,27 @@ def test_skipper():
     assert_raises(NameError, doctest_skip_parser, c)
 
 
+def test_test_parallel():
+    state = []
+
+    @test_parallel()
+    def change_state1():
+        state.append(None)
+    change_state1()
+    assert len(state) == 2
+
+    @test_parallel(num_threads=1)
+    def change_state2():
+        state.append(None)
+    change_state2()
+    assert len(state) == 3
+
+    @test_parallel(num_threads=3)
+    def change_state3():
+        state.append(None)
+    change_state3()
+    assert len(state) == 6
+
+
 if __name__ == '__main__':
     np.testing.run_module_suite()