zig/doc/langref/test_comptime_variables.zig

const std = @import("std");
const expectEqual = std.testing.expectEqual;

test "comptime vars" {
    var x: i32 = 1;
    comptime var y: i32 = 1;

    x += 1;
    y += 1;

    try expectEqual(2, x);
    try expectEqual(2, y);

    if (y != 2) {
        // This compile error never triggers because y is a comptime variable,
        // and so `y != 2` is a comptime value, and this if is statically evaluated.
        @compileError("wrong y value");
    }
}

// test