About the potential fix: I think the divCeil call should have a catch unreachable instead of a try. This is because divCeil can only fail when the denominator is zero (obviously) or between 1 and -1 (it could overflow). 16 cannot cause an error.

Just want to note that std.testing.expectEqualSlices doesn't exhibit this bug (dump_hex and expectEqualSlices don't share implementations):

const std = @import("std");

test {
    const bytes: []const u8 = &.{ 0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff, 0x01, 0x12, 0x13 };
    try std.testing.expectEqualSlices(u8, bytes, "");
}

Test [1/1] dump_hex.test_0... slices differ. first difference occurs at index 0 (0x0)

============ expected this output: =============  len: 19 (0x13)

00 11 22 33 44 55 66 77  88 99 AA BB CC DD EE FF  .."3DUfw........
01 12 13                                          ...

============= instead found this: ==============  len: 0 (0x0)



================================================

@squeek502 note that the std.testing function does not report the address of each 16-byte line which is where the bug is in std.debug.dump_hex

Oh, I was looking at the wrong thing. I saw the missing ... on the bottom line of the ouput.txt and thought that was the problem. Ignore me then