Add unit test for test_parallel decorator

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()