Nowadays there are so many external threats that can attack your PC that you need to be ready for any attack. To do this it is recommended to check for possible vulnerabilities in your PC, and more specifically in the firewall. This is why a tool like Leak Test exists.
Leak Test is a totally free utility that analyzes and checks your firewall looking for possible weaknesses and errors, or vulnerabilities it may have. This way you can verify that it is totally trustworthy and with no gaps.
Leak Test creates a report with all the information on your firewall, and of the programs that it blocked or allowed through.