OpenCV tests should not write any test results by default.

However sometimes it is useful to collect extra information for problem investigation (test failure).

• on devices/configurations without properly configured debugger
• on devices where compilation is not available (cross-compilation case) to modify test code or replace #if 0

Available options:

• --test_debug / --test_debug=N
• OPENCV_TEST_DEBUG environment variable
• variable cvtest::debugLevel

Note: Use debug mode for "debugging" single test case only. There is no requirement for unique filenames (result.png / test.png is a common practice).

Note: Use imshow() for debug levels >= 10 (to avoid test crashes due to lack of UI backend).