videoio: add routines to query information about backends API

into cv::videoio_registry namespace

modules/python/test/test_videoio.py

@@ -0,0 +1,25 @@
+#!/usr/bin/env python
+from __future__ import print_function
+
+import numpy as np
+import cv2 as cv
+
+from tests_common import NewOpenCVTests
+
+class Bindings(NewOpenCVTests):
+
+    def check_name(self, name):
+        #print(name)
+        self.assertFalse(name == None)
+        self.assertFalse(name == "")
+
+    def test_registry(self):
+        self.check_name(cv.videoio_registry.getBackendName(cv.CAP_ANY));
+        self.check_name(cv.videoio_registry.getBackendName(cv.CAP_FFMPEG))
+        self.check_name(cv.videoio_registry.getBackendName(cv.CAP_OPENCV_MJPEG))
+        backends = cv.videoio_registry.getBackends()
+        for backend in backends:
+            self.check_name(cv.videoio_registry.getBackendName(backend))
+
+if __name__ == '__main__':
+    NewOpenCVTests.bootstrap()