videoio(test): add "camera" tests

- disabled due specific requirements (camera, OpenNI camera, etc)
- designed for manual validation

modules/videoio/test/test_camera.cpp

+// This file is part of OpenCV project.
+// It is subject to the license terms in the LICENSE file found in the top-level directory
+// of this distribution and at http://opencv.org/license.html.
+
+// Note: all tests here are DISABLED by default due specific requirements.
+// Don't use #if 0 - these tests should be tested for compilation at least.
+//
+// Usage: opencv_test_videoio --gtest_also_run_disabled_tests --gtest_filter=*VideoIO_Camera*<tested case>*
+
+#include "test_precomp.hpp"
+
+namespace opencv_test { namespace {
+
+TEST(DISABLED_VideoIO_Camera, basic)
+{
+    VideoCapture capture(0);
+    ASSERT_TRUE(capture.isOpened());
+    std::cout << "Camera 0 via " << capture.getBackendName() << " backend" << std::endl;
+    std::cout << "Frame width: " << capture.get(CAP_PROP_FRAME_WIDTH) << std::endl;
+    std::cout << "     height: " << capture.get(CAP_PROP_FRAME_HEIGHT) << std::endl;
+    std::cout << "Capturing FPS: " << capture.get(CAP_PROP_FPS) << std::endl;
+
+    const int N = 100;
+    Mat frame;
+    int64 time0 = cv::getTickCount();
+    for (int i = 0; i < N; i++)
+    {
+        SCOPED_TRACE(cv::format("frame=%d", i));
+
+        capture >> frame;
+        ASSERT_FALSE(frame.empty());
+
+        EXPECT_GT(cvtest::norm(frame, NORM_INF), 0) << "Complete black image has been received";
+    }
+    int64 time1 = cv::getTickCount();
+    printf("Processed %d frames on %.2f FPS\n", N, (N * cv::getTickFrequency()) / (time1 - time0 + 1));
+
+    capture.release();
+}
+
+}} // namespace