Add tests for stateful kernel functionality

modules/gapi/misc/python/test/test_gapi_sample_pipelines.py

@@ -432,7 +432,7 @@ def test_invalid_op_input(self):
             with self.assertRaises(Exception): create_op([cv.GMat, int], [cv.GMat]).on(cv.GMat())
 
 
-        def test_stateful_kernel(self):
+        def test_state_in_class(self):
             @cv.gapi.op('custom.sum', in_types=[cv.GArray.Int], out_types=[cv.GOpaque.Int])
             class GSum:
                 @staticmethod

modules/gapi/misc/python/test/test_gapi_stateful_kernel.py

@@ -0,0 +1,96 @@
+#!/usr/bin/env python
+
+import numpy as np
+import cv2 as cv
+import os
+import sys
+import unittest
+
+from tests_common import NewOpenCVTests
+
+
+try:
+
+    if sys.version_info[:2] < (3, 0):
+        raise unittest.SkipTest('Python 2.x is not supported')
+
+
+    class CounterState:
+        def __init__(self):
+            self.counter = 0
+
+
+    @cv.gapi.op('stateful_counter',
+                in_types=[cv.GOpaque.Int],
+                out_types=[cv.GOpaque.Int])
+    class GStatefulCounter:
+        """Accumulate state counter on every call"""
+
+        @staticmethod
+        def outMeta(desc):
+            return cv.empty_gopaque_desc()
+
+
+    @cv.gapi.kernel(GStatefulCounter)
+    class GStatefulCounterImpl:
+        """Implementation for GStatefulCounter operation."""
+
+        @staticmethod
+        def setup(desc):
+            return CounterState()
+
+        @staticmethod
+        def run(value, state):
+            state.counter += value
+            return state.counter
+
+
+    class gapi_sample_pipelines(NewOpenCVTests):
+        def test_stateful_kernel_single_instance(self):
+            g_in  = cv.GOpaque.Int()
+            g_out = GStatefulCounter.on(g_in)
+            comp  = cv.GComputation(cv.GIn(g_in), cv.GOut(g_out))
+            pkg   = cv.gapi.kernels(GStatefulCounterImpl)
+
+            nums = [i for i in range(10)]
+            acc = 0
+            for v in nums:
+                acc = comp.apply(cv.gin(v), args=cv.gapi.compile_args(pkg))
+
+            self.assertEqual(sum(nums), acc)
+
+
+        def test_stateful_kernel_multiple_instances(self):
+            # NB: Every counter has his own independent state.
+            g_in   = cv.GOpaque.Int()
+            g_out0 = GStatefulCounter.on(g_in)
+            g_out1 = GStatefulCounter.on(g_in)
+            comp   = cv.GComputation(cv.GIn(g_in), cv.GOut(g_out0, g_out1))
+            pkg    = cv.gapi.kernels(GStatefulCounterImpl)
+
+            nums = [i for i in range(10)]
+            acc0 = acc1 = 0
+            for v in nums:
+                acc0, acc1 = comp.apply(cv.gin(v), args=cv.gapi.compile_args(pkg))
+
+            ref = sum(nums)
+            self.assertEqual(ref, acc0)
+            self.assertEqual(ref, acc1)
+
+
+except unittest.SkipTest as e:
+
+    message = str(e)
+
+    class TestSkip(unittest.TestCase):
+        def setUp(self):
+            self.skipTest('Skip tests: ' + message)
+
+        def test_skip():
+            pass
+
+    pass
+
+
+if __name__ == '__main__':
+    NewOpenCVTests.bootstrap()