Self-made app will not open
You should run the Snake.app/Contents/MacOS/Snake executable in Terminal to see if there's an error launching. 
Just Drag and drop it in Terminal and hit enter. If it launches, it's probably gatekeeper.

You can also check its permissions by running spctl -vv -a /path/to/app. If it is rejected, run 

spctl --add --label "LabelForMySnakeApp" /path/to/app
spctl --enable --label "LabelForMySnakeApp"



Block Specific Apps on macOS


Also see this question for some troubleshoot about codesign:


Gatekeeper refuses validly signed application