Factorial.zig

const std = @import("std");

pub fn factorial(n: u32) u32 {
    var result: u32 = 1;
    var i: u32 = 1;

    while (i <= n): (i += 1)
        result *= i;

    return result;
}

test "Test Factorial Base Case 1" {
    std.debug.assert(factorial(0) == 1);
}

test "Test Factorial Base Case 2" {
    std.debug.assert(factorial(1) == 1);
}

test "Test Factorial Normal Cases" {
    std.debug.assert(factorial(2) == 2);
    std.debug.assert(factorial(3) == 6);
    std.debug.assert(factorial(4) == 24);
    std.debug.assert(factorial(5) == 120);
    std.debug.assert(factorial(6) == 720);
    std.debug.assert(factorial(7) == 5040);
}

No problem :)