Backport of new python tests from master branch(PR https://github.com/Itseez/opencv/pull/6025).

At the moment tests requre samples/data copied to source location from master branch.

modules/python/test/test_watershed.py

@@ -0,0 +1,33 @@
+#!/usr/bin/env python
+
+'''
+Watershed segmentation test
+'''
+
+# Python 2/3 compatibility
+from __future__ import print_function
+
+import numpy as np
+import cv2
+
+from tests_common import NewOpenCVTests
+
+class watershed_test(NewOpenCVTests):
+    def test_watershed(self):
+
+        img = self.get_sample('cv/inpaint/orig.png')
+        markers = self.get_sample('cv/watershed/wshed_exp.png', 0)
+        refSegments = self.get_sample('cv/watershed/wshed_segments.png')
+
+        if img is None or markers is None:
+            self.assertEqual(0, 1, 'Missing test data')
+
+        colors = np.int32( list(np.ndindex(3, 3, 3)) ) * 122
+        cv2.watershed(img, np.int32(markers))
+        segments = colors[np.maximum(markers, 0)]
+
+        if refSegments is None:
+            refSegments = segments.copy()
+            cv2.imwrite(self.extraTestDataPath + '/cv/watershed/wshed_segments.png', refSegments)
+
+        self.assertLess(cv2.norm(segments - refSegments, cv2.NORM_L1) / 255.0, 50)