You can use null muxer to test it. As stated in Null - FFmpeg
The null muxer does not generate any output file. It is mainly useful for testing or benchmarking purposes.
This page provides a command line to check this out:
To test decoding and demuxing (using null muxer):
ffmpeg -i input -f null -
If your video is too short, you can try running a certain number of times. If you are using Windows, you can run cmd.exe and use the following to make the test 100 times:
for /l %a in (1,1,100) do ffmpeg -i input -f null -