Re: [PATCH v2 4/5] convert: generate large test files only once

> On 27 Jul 2016, at 15:32, Jeff King <peff@peff.net> wrote:
> 
> On Wed, Jul 27, 2016 at 04:35:32AM +0200, Torsten Bögershausen wrote:
> 
>>> +	mkdir -p generated-test-data &&
>>> +	for i in $(test_seq 1 $T0021_LARGE_FILE_SIZE)
>>> +	do
>>> +		# Generate 1MB of empty data and 100 bytes of random characters
>>> +		printf "%1048576d" 1
>>> +		printf "$(LC_ALL=C tr -dc "A-Za-z0-9" </dev/urandom | dd bs=$((RANDOM>>8)) count=1 2>/dev/null)"
>> I'm not sure how portable /dev/urandom is.
>> The other thing, that "really random" numbers are an overkill, and
>> it may be easier to use pre-defined numbers,
> 
> Right, there are a few reasons not to use /dev/urandom:
> 
>  - it's not portable
> 
>  - if we have to generate a lot of numbers, it drains the system's
>    entropy pool, which is an unfriendly thing to do (and may also be
>    slow)
> 
>  - it makes our tests random! This sounds like a good thing, but it
>    means that if some input happens to cause failure, you are unlikely
>    to be able to reproduce it.
> 
> Instead, use test-genrandom, which is an LCG that starts at a seed. So
> you get a large amount of random-ish quickly and portably, and you get
> the same data each time.