How do I run tests in `ReleaseFast` mode in Zig?

Question

Given that compiling in Debug or ReleaseFast mode may yield different results, I wanted to check if my library code works correctly and catch any bugs by using tests.

However, I couldn't find any option to tell tests to be compiled and run in ReleaseFast mode. I assume they are all running on Debug mode by default.

Answer 1

The options are exactly the same as if you were simply compiling the code.

Using the build system:

zig build test -Doptimize=ReleaseFast

Without the build system:

zig test ./test.zig -O ReleaseFast

As a proof of concept, this fails in Debug, but works in ReleaseFast:

test "should fail in debug" {
    var a = [3]u8{ 1, 2, 3 };
    var b: []u8 = a[0..2];
    var i: usize = 2;

    try std.testing.expect(b[i] == 3);
}

And here is one that fails in ReleaseFast but works in Debug:

fn getString() []u8 {
    var s: [32]u8 = undefined;
    s[0] = 'h';
    s[1] = 'e';
    s[2] = 'l';
    s[3] = 'o';
    return s[0..4];
}

test "should fail in release" {
    var s = getString();

    try std.testing.expectEqual(s[0], 'h');
    try std.testing.expectEqual(s[1], 'e');
    try std.testing.expectEqual(s[2], 'l');
    try std.testing.expectEqual(s[3], 'o');
}