I started to learn rust on the 1st of December so the quality of the code is not great especially for the first days.
To test the solution of the last day, run cargo run.
To test the solution of a specific day, run AOC_DAY=XX cargo run where "XX" is the day you want to test.
For example AOC_DAY=7 cargo run or AOC_DAY=05 cargo run or AOC_DAY=18 cargo run
You can specify the part you want to run with the --features flag for example cargo run --features "part1" to run only the first part.
You can also use the "small" feature to use the small input, for example AOC_DAY=14 cargo run --features "part2 small" to solve only the part2 of day 14 with the small input.