Test null plugin

skimage/io/tests/test_null.py

@@ -0,0 +1,35 @@
+import os
+import warnings
+
+import numpy as np
+from numpy.testing import raises
+
+from skimage import io
+from skimage import data_dir
+
+
+@raises(Warning)
+def test_null_imread():
+    path = os.path.join(data_dir, 'color.png')
+    with warnings.catch_warnings():  # Temporarily set warnings as errors.
+        warnings.filterwarnings('error')
+        io.imread(path, plugin='null')
+
+
+@raises(Warning)
+def test_null_imsave():
+    with warnings.catch_warnings():  # Temporarily set warnings as errors.
+        warnings.filterwarnings('error')
+        io.imsave('dummy.png', np.zeros((3, 3)), plugin='null')
+
+
+@raises(Warning)
+def test_null_imshow():
+    with warnings.catch_warnings():  # Temporarily set warnings as errors.
+        warnings.filterwarnings('error')
+        io.imshow(np.zeros((3, 3)), plugin='null')
+
+
+if __name__ == '__main__':
+    from numpy.testing import run_module_suite
+    run_module_suite()