I assume you have installed zig on your system.

$ zig build test

Build and install the executable

$ zig build

Execute it on the command line with an argument for the number of days:

$ ./zig/zig-out/bin/zig 10

There are instructions in the TextTest Readme for setting up TextTest. You will need to specify the executable in config.gr. Uncomment this line to use it:

#executable:${TEXTTEST_HOME}/zig/zig-out/bin/zig