Rebuild and test with make if any .c source files in the current directory change

Run arbitrary commands when files change.
More information: <https://manned.org/entr>.
Trick copyright: tl;dr; <https://github.com/tldr-pages/tldr>

{{ls *.c}} | entr {{'make && make test'}}

click the source code to copy install entr on any operating system with command-not-found.com